Implement the newly added ACLE functions for ld1/st1 with 2/3/4 vectors.
The functions are like: vst1_s8_x2 ...


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194990 91177308-0d34-0410-b5e6-96231b3b80d8