[Clang][VE] Add missing intrinsics

Add missing intrinsics and tests for them.  An expanding  macro
from _vel_pack_f32p to __builtin_ve_vl_pack_f32p and others is
already defined in clang/lib/Headers/velintrin.h.

Reviewed By: efocht

Differential Revision: https://reviews.llvm.org/D128120