[RISCV] Don't make it an error have Zve* and V at the same time.

This should not be an error. V is a valid implementation of Zve.

Spec clarified here
https://github.com/riscv/riscv-v-spec/commit/9a877e8553362ff03a9b22b98e321b59aff50398

Differential Revision: https://reviews.llvm.org/D118679