dt-bindings: riscv: Add pointer masking ISA extensions

The RISC-V Pointer Masking specification defines three extensions:
Smmpm, Smnpm, and Ssnpm. Document the behavior of these extensions as
following the ratified version 1.0 of the specification.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Link: https://lore.kernel.org/r/20241016202814.4061541-2-samuel.holland@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Documentation/devicetree/bindings/riscv/extensions.yaml

@@ -128,6 +128,18 @@ properties:
             changes to interrupts as frozen at commit ccbddab ("Merge pull
             request #42 from riscv/jhauser-2023-RC4") of riscv-aia.
 
+        - const: smmpm
+          description: |
+            The standard Smmpm extension for M-mode pointer masking as
+            ratified at commit d70011dde6c2 ("Update to ratified state")
+            of riscv-j-extension.
+
+        - const: smnpm
+          description: |
+            The standard Smnpm extension for next-mode pointer masking as
+            ratified at commit d70011dde6c2 ("Update to ratified state")
+            of riscv-j-extension.
+
         - const: smstateen
           description: |
             The standard Smstateen extension for controlling access to CSRs
@@ -147,6 +159,12 @@ properties:
             and mode-based filtering as ratified at commit 01d1df0 ("Add ability
             to manually trigger workflow. (#2)") of riscv-count-overflow.
 
+        - const: ssnpm
+          description: |
+            The standard Ssnpm extension for next-mode pointer masking as
+            ratified at commit d70011dde6c2 ("Update to ratified state")
+            of riscv-j-extension.
+
         - const: sstc
           description: |
             The standard Sstc supervisor-level extension for time compare as