[PowerPC][Power10] Exploit store rightmost vector element instructions

[PowerPC][Power10] Exploit store rightmost vector element instructions

Using the store rightmost vector element instructions to do vector
element extraction and store. The rightmost vector element on little
endian is the zeroth vector element, with these patterns that element
can be extracted and stored in one instruction for all vector types.

Differential Revision: https://reviews.llvm.org/D89195