[AArch64] Refines the Cortex-A57 Machine Model

Primarily refines all of the instructions with accurate latency
and micro-op information. Refinements largely focus on the NEON
instructions.

Additionally, a few advanced features are modeled, including
forwarding for MAC instructions and hazards for floating point SQRT
and DIV.

Lastly, the issue-width is reduced to three so that the scheduler
will better accommodate the narrower decode and dispatch width.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218627 91177308-0d34-0410-b5e6-96231b3b80d8