[Clang][RISCV] Simplify RVV intrinsic policy suffix

This patch works towards the simplification proposal [0] of Nick
Knight. After this patch, we have reduced the hierarchy of intrinsics
from two sets (non-policy and policy) into a single set, with a general
assumption that policy behavior is agnostic unless specified.

[0] https://gist.github.com/nick-knight/6cb0b74b351a25323dfb1821d3a269b9

Pull Request: riscv-non-isa/rvv-intrinsic-doc#186.

Depends on D141796.

Reviewed By: craig.topper, kito-cheng

Differential Revision: https://reviews.llvm.org/D142016