Revert "Fix new IT blocks ARMv8"

This reverts commit 90165c2269bc33ca3d6aaa73d528194daf48da4e.

Reason for revert: Skia and Chrome iOS builds broken.

../../third_party/skia/include/private/SkFixed.h:106:41: error: invalid output constraint '+t' in asm
        asm("vcvt.s32.f32 %0, %0, #16": "+t"(x));


Original change's description:
> Fix new IT blocks ARMv8
> 
> ARMv8 specifies that an IT block should be followed by only one 16-bit instruction.
> * SkFloatToFix is back to a C implementation that mirrors the assembly code.
> 
> * S32A_D565_Opaque_neon switched the usage of the temporary 'ip' register to let
> the compiler choose what is best in the context of the IT block. And replaced
> 'keep_dst' by 'ip' where low register or high register does not matter.
> 
> BUG=skia:
> 
> CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD
> 
> Change-Id: I096759841c972e9300c1d0293bc80d3c3ff2747b
> Reviewed-on: https://skia-review.googlesource.com/9340
> Reviewed-by: Mike Klein <mtklein@chromium.org>
> Commit-Queue: Mike Klein <mtklein@chromium.org>
> 

TBR=mtklein@chromium.org,amaury.leleyzour@arm.com,reviews@skia.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:
CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD

Change-Id: Idbcbda88039066153e1c34233d43366ab114fd01
Reviewed-on: https://skia-review.googlesource.com/9332
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
2 files changed