SkBitmapProcState_matrixProcs.cpp refactoring

 - Fold in _matrix_template.h
 - Make the NEON/non-NEON distictions a bit more clear.
 - Re-roll routines to their natural stride,
   leaving unrolling to the compiler.
 - Small style changes.
 - Leave some TODOs for another round.

Cq-Include-Trybots: luci.chromium.try:linux-blink-rel
Change-Id: Ide4111931aa5f19e23cac77722337ea5d53f72db
Reviewed-on: https://skia-review.googlesource.com/c/172020
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
5 files changed