[RISCV] Add riscv_vsoxei_mask/riscv_vsuxei_mask to getTgtMemIntrinsic.

This constructs a proper memory operand for riscv_vsoxei_mask and riscv_vsuxei_mask.
I think they are missed in D147119.

Reviewed By: kito-cheng

Differential Revision: https://reviews.llvm.org/D154694