arm: Optimize x264_deblock_h_chroma_neon

arm: Optimize x264_deblock_h_chroma_neon

Shuffle both chroma components together as a 16 bit unit, and
don't write the unchanged columns (like in x264_deblock_h_luma_neon
and in the aarch64 version of the function).

This causes a minor slowdown for x264_deblock_v_chroma_neon, but
it is negligible compared to the speedup.

checkasm timing      Cortex-A7    A8    A9
deblock_chroma[1]_c         4817  4057  3601
deblock_chroma[1]_neon      1249  716   817   (before)
deblock_chroma[1]_neon      1249  766   845   (after)

deblock_h_chroma_420_c      3699  3275  2830
deblock_h_chroma_420_neon   2068  1414  1400  (before)
deblock_h_chroma_420_neon   1838  1355  1291  (after)