[RISCV][llvm-mca] Add mca tests for riscv lmul instruments

Add llvm-mca tests for RISCV LMUL instruments to show that llvm-mca RISCV LMUL
instruments work.

This commit was previously reverted in 847789d4. It is now being
recommitted since the memory leak has been fixed in 4d2a1d7dd8f4.

Differential Revision: https://reviews.llvm.org/D149496