Turn on Sk4px xfermodes when we have NEON too.

Turn on Sk4px xfermodes when we have NEON too.

For SSE, Sk4px is better than Sk4f is better than SkXfermodes_opts_SSE2 (where implemented).
For NEON, Sk4px is better than SkXfermodes_opts_arm_neon is better than Sk4f (where implemented).

This is a 1.6-1.9x speedup for Plus,Modulate, and Screen for NEON.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/04d24a3f86b6f2382e5c6ffaf161ffc734a4d02a

[mtklein_C, 2015-05-12 21:30:30]

mtklein@chromium.org changed reviewers:
+ reed@google.com

[mtklein, 2015-05-12 22:48:43]

The CQ bit was checked by mtklein@google.com to run a CQ dry run

[commit-bot: I haz the power, 2015-05-12 22:49:03]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1128053004/1

[commit-bot: I haz the power, 2015-05-12 22:58:06]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-05-12 22:58:07]

Dry run: This issue passed the CQ dry run.

[reed1, 2015-05-13 14:57:22]

lgtm

[mtklein, 2015-05-13 15:01:41]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2015-05-13 15:01:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1128053004/1

[commit-bot: I haz the power, 2015-05-13 15:02:19]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/04d24a3f86b6f2382e5c6ffaf161ffc734a4d02a