Add divide to Sk2x, use native vdiv and vsqrt on ARM 64.

Add divide to Sk2x, use native vdiv and vsqrt on ARM 64.

Tests pass on N7 + N9.

BUG=skia:

CQ_EXTRA_TRYBOTS=client.skia.compile:Build-Mac10.7-Clang-Arm7-Debug-iOS-Trybot,Build-Ubuntu-GCC-Arm64-Release-Android-Trybot

Committed: https://skia.googlesource.com/skia/+/01a78130dc357e5ee746a37650dba622e0c07f8e

[mtklein_C, 2015-03-20 17:25:30]

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

[mtklein, 2015-03-20 17:25:57]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2015-03-20 17:26:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1027753003/1

[commit-bot: I haz the power, 2015-03-20 17:26:21]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from valid reviewer(s) till 2015-03-20 23:26 UTC

[reed1, 2015-03-20 18:26:56]

lgtm

[commit-bot: I haz the power, 2015-03-20 18:28:59]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/01a78130dc357e5ee746a37650dba622e0c07f8e