dct-test: test ff_simple_idct_neon only on ARM for now

Signed-off-by: Janne Grunau <janne-libav@jannau.net>
aarch64: add cpuflags support for NEON and VFP

NEON and VFP are currently mandatory for all ARMv8 profiles. Both are
handled as extensions as far as cpuflags are concerned. This is
consistent with handling x86_64 which always has SSE2, but still
handles it as an extension.
aarch64: h264 chroma motion compensation NEON optimizations

Since RV40 and VC-1 use almost the same algorithm so optimizations for
those two decoders are easy to do and included.
aarch64: h264 idct NEON assembler optimizations

Ported from ARMv7 NEON.
aarch64: h264 qpel NEON optimizations

Ported from ARMv7 NEON.
aarch64: hpeldsp NEON optimizations

Ported from ARMv7 NEON.
aarch64: h264 loop filter NEON optimizations

Ported from ARMv7 NEON.
aarch64: h264 (bi)weight NEON optimizations

Ported from ARMv7 NEON.
aarch64: port neon clobber test from arm