Test on Apple M1:

rgb24_to_uv_8_c: 0.0
rgb24_to_uv_8_neon: 0.2
rgb24_to_uv_128_c: 1.0
rgb24_to_uv_128_neon: 0.5
rgb24_to_uv_1080_c: 7.0
rgb24_to_uv_1080_neon: 5.7
rgb24_to_uv_1920_c: 12.5
rgb24_to_uv_1920_neon: 9.5
rgb24_to_uv_half_8_c: 0.2
rgb24_to_uv_half_8_neon: 0.2
rgb24_to_uv_half_128_c: 1.0
rgb24_to_uv_half_128_neon: 0.5
rgb24_to_uv_half_1080_c: 6.2
rgb24_to_uv_half_1080_neon: 3.0
rgb24_to_uv_half_1920_c: 11.2
rgb24_to_uv_half_1920_neon: 5.2
rgb24_to_y_8_c: 0.2
rgb24_to_y_8_neon: 0.0
rgb24_to_y_128_c: 0.5
rgb24_to_y_128_neon: 0.5
rgb24_to_y_1080_c: 4.7
rgb24_to_y_1080_neon: 3.2
rgb24_to_y_1920_c: 8.0
rgb24_to_y_1920_neon: 5.7

On Pixel 6:

rgb24_to_uv_8_c: 30.7
rgb24_to_uv_8_neon: 56.9
rgb24_to_uv_128_c: 213.9
rgb24_to_uv_128_neon: 173.2
rgb24_to_uv_1080_c: 1649.9
rgb24_to_uv_1080_neon: 1424.4
rgb24_to_uv_1920_c: 2907.9
rgb24_to_uv_1920_neon: 2480.7
rgb24_to_uv_half_8_c: 36.2
rgb24_to_uv_half_8_neon: 33.4
rgb24_to_uv_half_128_c: 167.9
rgb24_to_uv_half_128_neon: 99.4
rgb24_to_uv_half_1080_c: 1293.9
rgb24_to_uv_half_1080_neon: 778.7
rgb24_to_uv_half_1920_c: 2292.7
rgb24_to_uv_half_1920_neon: 1328.7
rgb24_to_y_8_c: 19.7
rgb24_to_y_8_neon: 27.7
rgb24_to_y_128_c: 129.9
rgb24_to_y_128_neon: 96.7
rgb24_to_y_1080_c: 995.4
rgb24_to_y_1080_neon: 767.7
rgb24_to_y_1920_c: 1747.4
rgb24_to_y_1920_neon: 1337.2

Note both tests use clang as compiler, which has vectorization
enabled by default with -O3.
Reviewed-by: Rémi Denis-Courmont <remi@remlab.net>
Reviewed-by: Martin Storsjö <martin@martin.st>
Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>