[AArch64] Lower 3 and 4 sources buildvectors to TBL

The default expansion for buildvectors is to extract each element and
insert them into a new vector. That involves a lot of copying to/from
the GPR registers. TLB3 and TLB4 can be relatively slow instructions
with the mask needing to be loaded from a constant pool, but they should
always be better than all the moves to/from GPRs.

Differential Revision: https://reviews.llvm.org/D121137