[PowerPC] Update P10 vector insert patterns to use refactored load/stores, and...

[PowerPC] Update P10 vector insert patterns to use refactored load/stores, and update handling of v4f32 vector insert.

This patch updates the P10 patterns with a load feeding into an insertelt to
utilize the refactored load and store infrastructure, as well as updating any
tests that exhibit any codegen changes.

Furthermore, custom legalization is added for v4f32 on Power9 and above to not
only assist with adjusting the refactored load/stores for P10 vector insert,
but also it enables the utilization of direct moves.

Differential Revision: https://reviews.llvm.org/D115691