[PowerPC] Implement low-order Vector Modulus Builtins, and add Vector...

[PowerPC] Implement low-order Vector Modulus Builtins, and add Vector Multiply/Divide/Modulus Builtins Tests

Power10 introduces new instructions for vector multiply, divide and modulus.
These instructions can be exploited by the builtin functions: vec_mul, vec_div,
and vec_mod, respectively.

This patch aims adds the function prototype, vec_mod, as vec_mul and vec_div
been previously implemented in altivec.h.

This patch also adds the following front end tests:
vec_mul for v2i64
vec_div for v4i32 and v2i64
vec_mod for v4i32 and v2i64

Differential Revision: https://reviews.llvm.org/D82576