Implement Zcmop Compressed MOP Instructions (#530)

This commit adds support for the Zcmop extension by defining the 16-bit compressed
C.MOP.n instructions. These instructions use a fixed encoding pattern with a variable
field (mop_n_field) to select one of eight instructions (for odd n values from 1 to 15).
By default, they do not write to any registers, which allows them to safely act as no-ops
when the extension is not active.

This change lays the foundation for future extensions that may redefine these instructions.

Co-authored-by: Afonso Oliveira <[email protected]>

Author: Shehrozkashif

arch/inst/Zcmop/c.mop.n.yaml

@@ -0,0 +1,38 @@
+# yaml-language-server: $schema=../../../schemas/inst_schema.json
+
+$schema: inst_schema.json#
+kind: instruction
+name: c.mop.n
+long_name: Compressed May-Be-Operation
+description: C.MOP.n is encoded in the reserved encoding space corresponding to C.LUI xn, 0. Unlike the MOPs defined in the Zimop extension, the C.MOP.n instructions are defined to not write any register. Their encoding allows future extensions to define them to read register x[n].
+definedBy: Zcmop
+assembly: ""
+encoding:
+  match: 01100---10000001
+  variables:
+    - name: n
+      location: 10-8
+access:
+  s: always
+  u: always
+  vs: always
+  vu: always
+data_independent_timing: false
+pseudoinstructions:
+  - when: (n == 0)
+    to: c.mop.1
+  - when: (n == 1)
+    to: c.mop.3
+  - when: (n == 2)
+    to: c.mop.5
+  - when: (n == 3)
+    to: c.mop.7
+  - when: (n == 4)
+    to: c.mop.9
+  - when: (n == 5)
+    to: c.mop.11
+  - when: (n == 6)
+    to: c.mop.13
+  - when: (n == 7)
+    to: c.mop.15
+operation(): "" #do nothing