dt-bindings: riscv: Add Zawrs ISA extension description

Add description for the Zawrs (Wait-on-Reservation-Set) ISA extension
which was ratified in commit 98918c844281 of riscv-isa-manual.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240426100820.14762-10-ajones@ventanamicro.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: Andrew Jones

Documentation/devicetree/bindings/riscv/extensions.yaml

@@ -177,6 +177,13 @@ properties:
             is supported as ratified at commit 5059e0ca641c ("update to
             ratified") of the riscv-zacas.
 
+        - const: zawrs
+          description: |
+            The Zawrs extension for entering a low-power state or for trapping
+            to a hypervisor while waiting on a store to a memory location, as
+            ratified in commit 98918c844281 ("Merge pull request #1217 from
+            riscv/zawrs") of riscv-isa-manual.
+
         - const: zba
           description: |
             The standard Zba bit-manipulation extension for address generation