[AArch64] Gangup loads and stores for pairing.

Keep loads and stores together (target defines how many loads
and stores to gang up), such that it will help in pairing
and vectorization.

Differential Revision https://reviews.llvm.org/D46477

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@332482 91177308-0d34-0410-b5e6-96231b3b80d8
10 files changed