[RISCV] Add a encodeLMUL function to RISCVVType. NFC

[craig.topper]

Summary

This moves the encoding handling out of the assembly parser.

[khchen]

LGTM, thanks!

llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp

if (VTypeIElements.size() == 7) {
     bool MaskAgnostic;
     if (Name == "ma")
       MaskAgnostic = true;
     else if (Name == "mu")
       MaskAgnostic = false;
     else
       goto MatchFail;
 
-    unsigned LmulLog2 = Log2_32(Lmul);
-    RISCVII::VLMUL VLMUL =
-        static_cast<RISCVII::VLMUL>(Fractional ? 8 - LmulLog2 : LmulLog2);
+    RISCVII::VLMUL VLMUL = RISCVVType::encodeLMUL(Lmul, Fractional);
 
     unsigned VTypeI =
         RISCVVType::encodeVTYPE(VLMUL, Sew, TailAgnostic, MaskAgnostic);
     Operands.push_back(RISCVOperand::createVType(VTypeI, S, isRV64()));
     return MatchOperand_Success;
   }
 
 // If NoMatch, unlex all the tokens that comprise a vtypei operand

llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h

 inline static RISCVII::VLMUL getVLMUL(unsigned VType) {
   unsigned VLMUL = VType & 0x7;
   return static_cast<RISCVII::VLMUL>(VLMUL);
 }
 
 // Decode VLMUL into 1,2,4,8 and fractional indicator.
 std::pair<unsigned, bool> decodeVLMUL(RISCVII::VLMUL VLMUL);
 
+inline static RISCVII::VLMUL encodeLMUL(unsigned LMUL, bool Fractional) {
+  assert(isValidLMUL(LMUL, Fractional) && "Unsupported LMUL");
+  unsigned LmulLog2 = Log2_32(LMUL);
+  return static_cast<RISCVII::VLMUL>(Fractional ? 8 - LmulLog2 : LmulLog2);
+}
+
 inline static unsigned decodeVSEW(unsigned VSEW) {
   assert(VSEW < 8 && "Unexpected VSEW value");
   return 1 << (VSEW + 3);
 }
 
 inline static unsigned encodeSEW(unsigned SEW) {
   assert(isValidSEW(SEW) && "Unexpected SEW value");
   return Log2_32(SEW) - 3;