SkJumper: a couple stages used by color filters

SkJumper: a couple stages used by color filters

Nothing too interesting here.
  - 4x5 matrix is the same as 2x3 and 3x4, but bigger.
  - luminance to alpha is pretty boring indeed.

Change-Id: I24893df15d1e22cbb500d946e1bbb58aa1522c8c
Reviewed-on: https://skia-review.googlesource.com/9385
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>