[RISCV][Clang] Teach RISCVEmitter to generate BitCast for pointer operands.

RVV C intrinsics use pointers to scalar for base address and their corresponding
IR intrinsics but use pointers to vector. It makes some vector load intrinsics
need specific ManualCodegen and MaskedManualCodegen to just add bitcast for
transforming to IR.

For simplifying riscv_vector.td, the patch make RISCVEmitter detect pointer
operands and bitcast them.

Reviewed By: kito-cheng

Differential Revision: https://reviews.llvm.org/D129043