dec_neon: (WORK_AROUND_GCC) delete unused Load4x8

using this in Load4x16 was slightly slower and didn't help mitigate any
of the remaining build issues with 4.6.x.

Change-Id: Idabfe1b528842a514d14a85f4cefeb90abe08e51
enc_neon: move Transpose4x4 to dsp/neon.h

+ reuse it in TransformWHT()

Change-Id: Idfbd0f9b58d6253ac3d65ba55b58989c427ee989
move LOCAL_GCC_VERSION def to dsp.h

+ add LOCAL_GCC_PREREQ and use it in lossless_neon.c

Change-Id: Ic9fd99540bc3e19c027d1598e4530dfdc9b9de00
enc_neon: enable intrinsics-only functions

CollectHistogram / SSE* / QuantizeBlock have no inline equivalents,
enable them where possible and use USE_INTRINSICS to control borderline
cases: it's left undefined for now.

Change-Id: I62235bc4ddb8aa0769d1ce18a90e0d7da1e18155
fix warning about size_t -> int conversion

+ re-order and add some const

Change-Id: I3746520b75699e56e20835d10d1dd9cd9fd6d85d
Merge "fix warning about size_t -> int conversion"
Merge "enc_neon: move Transpose4x4 to dsp/neon.h"
Merge "move LOCAL_GCC_VERSION def to dsp.h"
Merge "enc_neon: enable intrinsics-only functions"