[PowerPC] Add target feature requirement to builtins

Clang has mechanism to specify required target features of a built-in
function. This patch adds such definitions to Altivec, VSX, HTM,
PairedVec and MMA builtins.

This will help frontend to detect incompatible target features of
bulitin when using target attribute syntax.

Reviewed By: nemanjai, kamaub

Differential Revision: https://reviews.llvm.org/D143467