Add SiFive Intelligence Extensions

Added 4 extensions from xsfvfnrclipxfqf, xsfvfwmaccqqq, xsfvqmaccdod and
xsfvqmaccqoq, specs are publicly accessible, also we have support that
on upstream LLVM already.

We'll upstream those extension to GNU toolchain as well soon.

Author: kito-cheng

README.mkd

@@ -319,6 +319,10 @@ OpenHW  | Xcvhwlp         | 1.0.0          | [CORE-V Instruction Set Extensions]
 OpenHW  | Xcvmac          | 1.0.0          | [CORE-V Instruction Set Extensions](https://github.com/openhwgroup/cv32e40p/blob/dev/docs/source/instruction_set_extensions.rst)
 OpenHW  | Xcvmem          | 1.0.0          | [CORE-V Instruction Set Extensions](https://github.com/openhwgroup/cv32e40p/blob/dev/docs/source/instruction_set_extensions.rst)
 OpenHW  | Xcvsimd         | 1.0.0          | [CORE-V Instruction Set Extensions](https://github.com/openhwgroup/cv32e40p/blob/dev/docs/source/instruction_set_extensions.rst)
+SiFive  | XSFvqmaccdod    | 1.0            | [SiFive Int8 Matrix Multiplication Extensions Specification](https://www.sifive.com/document-file/sifive-int8-matrix-multiplication-extensions-specification)
+SiFive  | XSFvqmaccqoq    | 1.0            | [SiFive Int8 Matrix Multiplication Extensions Specification](https://www.sifive.com/document-file/sifive-int8-matrix-multiplication-extensions-specification)
+SiFive  | XSFvfnrclipxfqf | 1.0            | [FP32-to-int8 Ranged Clip Instructions (Xsfvfnrclipxfqf) Extension Specification](https://www.sifive.com/document-file/fp32-to-int8-ranged-clip-instructions)
+SiFive  | Xsfvfwmaccqqq   | 1.0            | [Matrix Multiply Accumulate Instruction (Xsfvfwmaccqqq) Extension Specification](https://www.sifive.com/document-file/matrix-multiply-accumulate-instruction)
 SiFive  | XSFVCP          | 1.0            | [SiFive Vector Coprocessor Interface Software Specification](https://sifive.cdn.prismic.io/sifive/c3829e36-8552-41f0-a841-79945784241b_vcix-spec-software.pdf)
 T-Head  | XTheadCmo       | 1.0            | [T-Head ISA extension specification](https://github.com/T-head-Semi/thead-extension-spec/releases/latest)
 T-Head  | XTheadBa        | 1.0            | [T-Head ISA extension specification](https://github.com/T-head-Semi/thead-extension-spec/releases/latest)