[AMDGPU] Add documentation files for GFX12.

This patch contains newly created documentation files for GFX12
instructions. The file AMDGPUAsmGFX12.rst lists all the instructions,
while the rest, with the gfx12_ filename prefix, are for various
instruction operands. A few existing files are also updated.

Author: jwanggit86

llvm/docs/AMDGPU/AMDGPUAsmGFX12.rst

@@ -0,0 +1,15 @@
+..
+    **************************************************
+    *                                                *
+    *   Automatically generated file, do not edit!   *
+    *                                                *
+    **************************************************
+
+.. _amdgpu_synid_gfx12_addr:
+
+addr
+====
+
+*Size:* 1 dword.
+
+*Operands:* :ref:`v<amdgpu_synid_v>`

llvm/docs/AMDGPU/gfx12_addr.rst

@@ -0,0 +1,28 @@
+..
+    **************************************************
+    *                                                *
+    *   Automatically generated file, do not edit!   *
+    *                                                *
+    **************************************************
+
+.. _amdgpu_synid_gfx12_attr:
+
+attr
+====
+
+Interpolation attribute and channel:
+
+    ============== ===================================
+    Syntax         Description
+    ============== ===================================
+    attr{0..32}.x  Attribute 0..32 with *x* channel.
+    attr{0..32}.y  Attribute 0..32 with *y* channel.
+    attr{0..32}.z  Attribute 0..32 with *z* channel.
+    attr{0..32}.w  Attribute 0..32 with *w* channel.
+    ============== ===================================
+
+Examples:
+
+.. parsed-literal::
+
+    ds_param_load v1, attr0.x

llvm/docs/AMDGPU/gfx12_attr.rst

@@ -0,0 +1,7 @@
+.. _amdgpu_synid_clause:
+
+clause
+======
+
+Description of a clause following this instruction.
+

llvm/docs/AMDGPU/gfx12_clause.rst

@@ -0,0 +1,17 @@
+..
+    **************************************************
+    *                                                *
+    *   Automatically generated file, do not edit!   *
+    *                                                *
+    **************************************************
+
+.. _amdgpu_synid_gfx12_data0_56f215:
+
+data0
+=====
+
+Instruction input.
+
+*Size:* 3 dwords.
+
+*Operands:* :ref:`v<amdgpu_synid_v>`

llvm/docs/AMDGPU/gfx12_data0_56f215.rst

@@ -0,0 +1,17 @@
+..
+    **************************************************
+    *                                                *
+    *   Automatically generated file, do not edit!   *
+    *                                                *
+    **************************************************
+
+.. _amdgpu_synid_gfx12_data0_6802ce:
+
+data0
+=====
+
+Instruction input.
+
+*Size:* 1 dword.
+
+*Operands:* :ref:`v<amdgpu_synid_v>`

llvm/docs/AMDGPU/gfx12_data0_6802ce.rst

@@ -0,0 +1,17 @@
+..
+    **************************************************
+    *                                                *
+    *   Automatically generated file, do not edit!   *
+    *                                                *
+    **************************************************
+
+.. _amdgpu_synid_gfx12_data0_e016a1:
+
+data0
+=====
+
+Instruction input.
+
+*Size:* 4 dwords.
+
+*Operands:* :ref:`v<amdgpu_synid_v>`

llvm/docs/AMDGPU/gfx12_data0_e016a1.rst

@@ -0,0 +1,17 @@
+..
+    **************************************************
+    *                                                *
+    *   Automatically generated file, do not edit!   *
+    *                                                *
+    **************************************************
+
+.. _amdgpu_synid_gfx12_data0_fd235e:
+
+data0
+=====
+
+Instruction input.
+
+*Size:* 2 dwords.
+
+*Operands:* :ref:`v<amdgpu_synid_v>`

llvm/docs/AMDGPU/gfx12_data0_fd235e.rst

@@ -0,0 +1,17 @@
+..
+    **************************************************
+    *                                                *
+    *   Automatically generated file, do not edit!   *
+    *                                                *
+    **************************************************
+
+.. _amdgpu_synid_gfx12_data1_6802ce:
+
+data1
+=====
+
+Instruction input.
+
+*Size:* 1 dword.
+
+*Operands:* :ref:`v<amdgpu_synid_v>`

llvm/docs/AMDGPU/gfx12_data1_6802ce.rst

@@ -0,0 +1,17 @@
+..
+    **************************************************
+    *                                                *
+    *   Automatically generated file, do not edit!   *
+    *                                                *
+    **************************************************
+
+.. _amdgpu_synid_gfx12_data1_731030:
+
+data1
+=====
+
+Instruction input.
+
+*Size:* 8 dwords.
+
+*Operands:* :ref:`v<amdgpu_synid_v>`