[RISCV] Use tail agnostic policy when selecting riscv_fma_vl to instructions

riscv_fma_vl doesn't have a tail, so use the tail_agnostic policy.

We were already doing this for some patterns. I think the patterns
with fneg and mask were added later and I copied the tail policy
from the unmasked patterns.

Reviewed By: khchen

Differential Revision: https://reviews.llvm.org/D125424