[RISCV] Add OperandType to loadfpimm. (llvm#114150)

This is represented in the MachineInstr and MCInst as a 5-bit unsigned
immediate so we use OPERAND_UIMM5. If someone needs to know for sure its
an FLI constant in the future we can break it out to a new type.

(This is a cherry-pick of c62130f)

Author: topperc

llvm/lib/Target/RISCV/RISCVInstrInfoZfa.td

@@ -26,6 +26,8 @@ def LoadFPImmOperand : AsmOperandClass {
 def loadfpimm : Operand<XLenVT> {
   let ParserMatchClass = LoadFPImmOperand;
   let PrintMethod = "printFPImmOperand";
+  let OperandType = "OPERAND_UIMM5";
+  let OperandNamespace = "RISCVOp";
 }
 
 def RTZArg : AsmOperandClass {