[RISCV] Support scalar/fix-length vector NTLH intrinsic with different domain

[BeMg]

Summary

This commit implements the two NTLH intrinsic functions.

type __rv_ntl_load (type *ptr, int domain);
void __rv_ntl_store (type *ptr, type val, int domain);

enum {
  __RISCV_NTLH_INNERMOST_PRIVATE = 2,
  __RISCV_NTLH_ALL_PRIVATE,
  __RISCV_NTLH_INNERMOST_SHARED,
  __RISCV_NTLH_ALL
};

We encode the non-temporal domain into MachineMemOperand flags.

1. Create the RISC-V built-in function with custom semantic checking.
2. Assume the domain argument is a compile time constant,

and make it as LLVM IR metadata (nontemp_node).

3. Encode domain value as two bits MachineMemOperand TargetMMOflag.
4. According to MachineMemOperand TargetMMOflag, select corrsponding ntlh instruction.

Currently, it supports scalar type and fixed-length vector type.