Revert of SkPx: new approach to fixed-point SIMD

Revert of SkPx: new approach to fixed-point SIMD (patchset #9 id:160001 of https://codereview.chromium.org/1317233005/ )

Reason for revert:
http://build.chromium.org/p/client.skia.compile/builders/Build-Mac10.8-Clang-Arm7-Debug-Android/builds/4627

Original issue's description:
> SkPx: new approach to fixed-point SIMD
> 
> SkPx is like Sk4px, except each platform implementation of SkPx can declare
> a different sweet spot of N pixels, with extra loads and stores to handle the 
> ragged edge of 0<n<N pixels.
> 
> In this case, _sse's sweet spot remains 4 pixels.   _neon jumps up to 8 so
> we can now use NEON's transposing loads and stores, and _none is just 1.
> This makes operations involving alpha considerably more efficient on NEON,
> as alpha is its own distinct 8x8 bit plane that's easy to toss around.
> 
> This incorporates a few other improvements I've been wanting:
>   - no requirement that we're dealing with SkPMColor.  SkColor works too.
>   - no anonymous namespace hack to differentiate implementations.
> 
> Codegen and perf look good on Clang/x86-64 and GCC/ARMv7.
> The NEON code looks very similar to the old NEON code, as intended.
> No .skp or GM diffs on my laptop.  Don't expect any.
> 
> I intend this to replace Sk4px.  Plan after landing:
>   - port SkXfermode_opts.h
>   - port Color32 in SkBlitRow_D32.cpp (and move to SkBlitRow_opts.h like other
>     SkOpts code)
>   - delete all Sk4px-related code
>   - clean up evolutionary dead ends in SkNx (Sk16b, Sk16h, Sk4i, Sk4d, etc.)
>     leaving Sk2f, Sk4f (and Sk2s, Sk4s).
>   - find a machine with AVX2 to work on, write SkPx_avx2.h handling 8 pixels
>     at a time.
> 
> In the end we'll have Sk4f for float pixels, SkPx for fixed-point pixels.
> 
> BUG=skia:4117
> 
> Committed: https://skia.googlesource.com/skia/+/82c93b45ed6ac0b628adb8375389c202d1f586f9

TBR=mtklein@google.com,msarett@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:4117
Committed: https://skia.googlesource.com/skia/+/07344a5386b70f682b16b40bc6eb83acf76d6921

[mtklein_C, 2015-09-14 20:14:09]

Created Revert of SkPx: new approach to fixed-point SIMD

[commit-bot: I haz the power, 2015-09-14 20:14:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1336423002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1336423002/1

[commit-bot: I haz the power, 2015-09-14 20:14:34]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/07344a5386b70f682b16b40bc6eb83acf76d6921