[AArch64] Rename AArch64VecorByElementOpt.cpp into AArch64SIMDInstrOpt.cpp to reflect the recently added features.

The name change is dicsussed in https://reviews.llvm.org/D38196

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@320204 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed