[PowerPC] Add range checks for P10 Vector Builtins
This patch adds range checking for some Power10 altivec builtins and
changes the signature of a builtin to match documentation. For vec_cntm,
range checking is done via SemaChecking. For vec_splati_ins, the second
argument is masked to extract the 0th bit so that we always receive either a 0
or a 1.
Reviewed By: lei, amyk
Differential Revision: https://reviews.llvm.org/D109710