[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.