[RISCV][llvm-mca] Use correct LMUL and SEW for strided loads and stores (#76869)

The pseudos for strided loads and stores use the SEW coming from the
name. For example, vlse8 has SEW=8 and vlse16 has SEW=16.

When llvm-mca tries to lookup (VLSE8_V, SEW=S, LMUL=L) in the inverse
pseudo table, a result will only be found when S=8, where S was set from
the previous vsetvli instruction. Instead, for a match to be found, we
must lookup (VLSE8_V, SEW=8, LMUL=L') where L' is the EMUL which was
calculated by scaling the LMUL and SEW from the previous vsetvli and the
SEW=8.