[AArch64] Fix a pattern match failure caused by creating improper CONCAT_VECTOR.

ReconstructShuffle() may wrongly creat a CONCAT_VECTOR trying to
concat 2 of v2i32 into v4i16. This commit is to fix this issue and
try to generate UZP1 instead of lots of MOV and INS.
Patch is initalized by Kevin Qin, and refactored by Tim Northover.

llvm-svn: 211144