Revert of ARM Skia NEON patches - 35 - First AArch64 support

Revert of ARM Skia NEON patches - 35 - First AArch64 support (https://codereview.chromium.org/143423004/)

Reason for revert:
GYP's failing on most (all?) bots.

Original issue's description:
> ARM Skia NEON patches - 35 - First AArch64 support
> 
> Aarch64 support
> 
> This change contains the necessary modifications to have Skia build and
> run properly on an ARMv8 processor in aarch64 execution state.
> 
> Here's a list of the changes:
> 
>  - add an arm64 target to the build system + SK_CPU_ARM64 flag
> 
>  - MatrixTest was failing when built in Release mode. Fused MAC
>    instructions were generated which made some intermediate results
>    more accurate. As the test relies on result comparison, the more
>    precise results when compared to others led to a gap bigger than
>    what was tolerated. As I don't know if some actual skia code relies
>    on results being comparable, I've disabled fused MAC instruction
>    with -ffp-contract=off for arm64.
> 
>  - Modify include/core/SkOnce.h to have barriers work.
> 
>  - SK_CPU_ARM64 implies SK_ARM_NEON_MODE_ALWAYS.
> 
>  - use existing Xfermode optimisations with modifications that can be
>    removed in the future when toolchains are ready. Also save a few
>    instructions is two Xfermodes (will apply to ARM too).
> 
>  - use existing SkBoxBlur and SkMorphology optimisations.
> 
>  - use existing SkBlitMask optimisations
> 
>  - use existing BitmapProcState and Convolution optimisations.
> 
> Future changes will include:
> 
>  - Blitters (only partialy merged upstream)
> 
>  - SkUtils (there's little value in sending asm optimisations without
>    having them benchmarked on real hardware).
> 
> Signed-off-by: Kevin PETIT <kevin.petit@arm.com>;
> 
> BUG=skia:
> 
> Committed: http://code.google.com/p/skia/source/detail?r=13980

TBR=djsollen@google.com,reed@google.com,halcanary@google.com,kevin.petit@arm.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Committed: http://code.google.com/p/skia/source/detail?r=13983

[mtklein, 2014-03-28 18:05:14]

Created Revert of ARM Skia NEON patches - 35 - First AArch64 support

[commit-bot: I haz the power, 2014-03-28 18:05:20]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/mtklein@google.com/216113005/1

[commit-bot: I haz the power, 2014-03-28 18:05:41]

Change committed as 13983