[AMDGPU] Update AMDGPUUsage.rst to document two intrinsics (llvm#123816)

The AMDGPUUsage.rst file is updated to document two intrinsics:
llvm.amdgcn.mov.dpp and llvm.amdgcn.update.dpp.

Author: jwanggit86

llvm/docs/AMDGPUUsage.rst

@@ -1422,6 +1422,19 @@ The AMDGPU backend implements the following LLVM IR intrinsics.
                                                    Returns a pair for the swapped registers. The first element of the return
                                                    corresponds to the swapped element of the first argument.
 
+  llvm.amdgcn.mov.dpp                              The llvm.amdgcn.mov.dpp.`<type>` intrinsic represents the mov.dpp operation in AMDGPU.
+                                                   This operation is being deprecated and can be replaced with llvm.amdgcn.update.dpp.
+
+  llvm.amdgcn.update.dpp                           The llvm.amdgcn.update.dpp.`<type>` intrinsic represents the update.dpp operation in AMDGPU.
+                                                   It takes an old value, a source operand, a DPP control operand, a row mask, a bank mask, and a bound control.
+                                                   Various data types are supported, including, bf16, f16, f32, f64, i16, i32, i64, p0, p3, p5, v2f16, v2f32, v2i16, v2i32, v2p0, v3i32, v4i32, v8f16.
+                                                   This operation is equivalent to a sequence of v_mov_b32 operations.
+                                                   It is preferred over llvm.amdgcn.mov.dpp.`<type>` for future use.
+                                                   `llvm.amdgcn.update.dpp.<type> <old> <src> <dpp_ctrl> <row_mask> <bank_mask> <bound_ctrl>`
+                                                   Should be equivalent to:
+                                                   - `v_mov_b32 <dest> <old>`
+                                                   - `v_mov_b32 <dest> <src> <dpp_ctrl> <row_mask> <bank_mask> <bound_ctrl>`
+
   ==============================================   ==========================================================
 
 .. TODO::