[RISCV] Enable more builtin for zvfhmin without zvfh

This patch enables some fp16 vector type builtins that don't use fp arithmetic instruction for zvfhmin without zvfh.
Include following builtins:
  vector load/store,
  vector reinterpret,
  vmerge_vvm,
  vmv_v.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D151869