dt-bindings: riscv: Add xsfvfnrclipxfqf ISA extension description

Add "xsfvfnrclipxfqf" ISA extension which is provided by SiFive for
FP32-to-int8 ranged clip instructions support.

Signed-off-by: Cyan Yang <cyan.yang@sifive.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250418053239.4351-6-cyan.yang@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: cyanyang-sifive

Documentation/devicetree/bindings/riscv/extensions.yaml

@@ -675,6 +675,12 @@ properties:
             See more details in
             https://www.sifive.com/document-file/sifive-int8-matrix-multiplication-extensions-specification
 
+        - const: xsfvfnrclipxfqf
+          description:
+            SiFive FP32-to-int8 Ranged Clip Instructions Extensions Specification.
+            See more details in
+            https://www.sifive.com/document-file/fp32-to-int8-ranged-clip-instructions
+
         # T-HEAD
         - const: xtheadvector
           description: