[PowerPC] Implement Vector Multiply High/Divide Extended Builtins in LLVM/Clang

This patch implements the function prototypes vec_mulh and vec_dive in order to
utilize the vector multiply high (vmulh[s|u][w|d]) and vector divide extended
(vdive[s|u][w|d]) instructions introduced in Power10.

Differential Revision: https://reviews.llvm.org/D82609