add 'a8' config for nanobench, specialize blitV for raster-pipeline

Motivated by wanting to speed-up A8 blits in general (and at the moment, aarect blits). More to come in these areas.

Bug: skia:
Change-Id: I45e8ef951b8e89a825af72b1918049be10920137
Reviewed-on: https://skia-review.googlesource.com/39401
Reviewed-by: Yuqian Li <liyuqian@google.com>
Commit-Queue: Mike Reed <reed@google.com>
2 files changed