dt-bindings: riscv: add Zimop ISA extension description

Add description for the Zimop (May-Be-Operations) ISA extension which
was ratified in commit 58220614a5f of the riscv-isa-manual.
Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240619113529.676940-2-cleger@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Documentation/devicetree/bindings/riscv/extensions.yaml

@@ -363,6 +363,11 @@ properties:
             ratified in the 20191213 version of the unprivileged ISA
             specification.
 
+        - const: zimop
+          description:
+            The standard Zimop extension version 1.0, as ratified in commit
+            58220614a5f ("Zimop is ratified/1.0") of the riscv-isa-manual.
+
         - const: ztso
           description:
             The standard Ztso extension for total store ordering, as ratified