[flang] Add PowerPC vec_extract, vec_insert, vec_mergeh, vec_mergel, vec_perm...

[flang] Add PowerPC vec_extract, vec_insert, vec_mergeh, vec_mergel, vec_perm and ver_permi intrinsic

Co-authored-by: Paul Scoropan <1paulscoropan@gmail.com>
Co-authored-by: Mark Danial <Mark.Danial@ibm.com>

Differential Revision: https://reviews.llvm.org/D156197