dt-bindings: riscv: document vector crypto requirements

The Unpriv spec states:
| The Zvknhb and Zvbc Vector Crypto Extensions --and accordingly the
| composite extensions Zvkn, Zvknc, Zvkng, and Zvksc-- require a Zve64x
| base, or application ("V") base Vector Extension. All of the other
| Vector Crypto Extensions can be built on any embedded (Zve*) or
| application ("V") base Vector Extension.

Enforce the minimum requirement via schema.

Link: https://github.com/riscv/riscv-isa-manual/blob/main/src/vector-crypto.adoc#extensions-overview
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250312-flask-relay-b36ee622b2c8@spud
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Documentation/devicetree/bindings/riscv/extensions.yaml

@@ -726,6 +726,39 @@ properties:
             - contains:
                 const: zve64f
 
+      - if:
+          contains:
+            anyOf:
+              - const: zvbc
+              - const: zvkn
+              - const: zvknc
+              - const: zvkng
+              - const: zvknhb
+              - const: zvksc
+        then:
+          contains:
+            anyOf:
+              - const: v
+              - const: zve64x
+
+      - if:
+          contains:
+            anyOf:
+              - const: zvbb
+              - const: zvkb
+              - const: zvkg
+              - const: zvkned
+              - const: zvknha
+              - const: zvksed
+              - const: zvksh
+              - const: zvks
+              - const: zvkt
+        then:
+          contains:
+            anyOf:
+              - const: v
+              - const: zve32x
+
 allOf:
   # Zcf extension does not exist on rv64
   - if: