[clang] [llvm] [RISC-V] Added the mips extension instructions like ehb,ihb and pause etc for MIPS RV64 P8700. (PR #155747)

[Craig Topper via llvm-commits]

================
@@ -125,10 +125,25 @@ class Mips_prefetch_ri<dag outs, dag ins, string opcodestr, string argstr>
   let Inst{6-0} = OPC_CUSTOM_0.Value;
 }
 
+// MIPS Ext Insns Fromat.
----------------
topperc wrote:

```suggestion
// MIPS Ext Insns Format.
```

https://github.com/llvm/llvm-project/pull/155747