dt-bindings: riscv: permit numbers in "riscv,isa"

There are some extensions that contain numbers, such as Zve32f, which
are enabled by the "max" cpu type in QEMU.
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231208-uncolored-oxidant-5ab37dd3ab84@spudSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Documentation/devicetree/bindings/riscv/extensions.yaml

@@ -48,7 +48,7 @@ properties:
       insensitive, letters in the riscv,isa string must be all
       lowercase.
     $ref: /schemas/types.yaml#/definitions/string
-    pattern: ^rv(?:64|32)imaf?d?q?c?b?k?j?p?v?h?(?:[hsxz](?:[a-z])+)?(?:_[hsxz](?:[a-z])+)*$
+    pattern: ^rv(?:64|32)imaf?d?q?c?b?k?j?p?v?h?(?:[hsxz](?:[0-9a-z])+)?(?:_[hsxz](?:[0-9a-z])+)*$
     deprecated: true
 
   riscv,isa-base: