dt-bindings: riscv: Add Svvptc ISA extension description

Add description for the Svvptc ISA extension which was ratified recently.
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240717060125.139416-3-alexghiti@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Documentation/devicetree/bindings/riscv/extensions.yaml

@@ -171,6 +171,13 @@ properties:
             memory types as ratified in the 20191213 version of the privileged
             ISA specification.
 
+        - const: svvptc
+          description:
+            The standard Svvptc supervisor-level extension for
+            address-translation cache behaviour with respect to invalid entries
+            as ratified at commit 4a69197e5617 ("Update to ratified state") of
+            riscv-svvptc.
+
         - const: zacas
           description: |
             The Zacas extension for Atomic Compare-and-Swap (CAS) instructions