riscv: hwprobe: Document SiFive xsfvfnrclipxfqf vendor extension

Document the support for SiFive vendor extensions for
FP32-to-int8 Ranged Clip Instructions using
RISCV_HWPROBE_VENDOR_EXT_XSFVFNRCLIPXFQF.

Signed-off-by: Cyan Yang <cyan.yang@sifive.com>
Link: https://lore.kernel.org/r/20250418053239.4351-8-cyan.yang@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: cyanyang-sifive

Documentation/arch/riscv/hwprobe.rst

@@ -349,3 +349,7 @@ The following keys are defined:
     * :c:macro:`RISCV_HWPROBE_VENDOR_EXT_XSFVQMACCQOQ`: The Xsfqmaccqoq vendor
         extension is supported in version 1.1 of SiFive Int8 Matrix Multiplication
 	Instruction Extensions Specification.
+
+    * :c:macro:`RISCV_HWPROBE_VENDOR_EXT_XSFVFNRCLIPXFQF`: The Xsfvfnrclipxfqf
+        vendor extension is supported in version 1.0 of SiFive FP32-to-int8 Ranged
+	Clip Instructions Extensions Specification.