[RISCV] Add support for fixed vector MULHU/MULHS.

This uses to division by constant optimization to use MULHU/MULHS.

Reviewed By: frasercrmck, arcbbb

Differential Revision: https://reviews.llvm.org/D96934

GitOrigin-RevId: 156fc07e19ae599e638e18e598dbf5c5a4247408
4 files changed