This work is sponsored by, and copyright, Google.

This has mostly got the same differences to the 8 bit version as
in the arm version. For the horizontal filters, we do 16 pixels
in parallel as well. For the 8 pixel wide vertical filters, we can
accumulate 4 rows before storing, just as in the 8 bit version.

Examples of runtimes vs the 32 bit version, on a Cortex A53:
                                           ARM   AArch64
vp9_avg4_10bpp_neon:                      35.7      30.7
vp9_avg8_10bpp_neon:                      93.5      84.7
vp9_avg16_10bpp_neon:                    324.4     296.6
vp9_avg32_10bpp_neon:                   1236.5    1148.2
vp9_avg64_10bpp_neon:                   4639.6    4571.1
vp9_avg_8tap_smooth_4h_10bpp_neon:       130.0     128.0
vp9_avg_8tap_smooth_4hv_10bpp_neon:      440.0     440.5
vp9_avg_8tap_smooth_4v_10bpp_neon:       114.0     105.5
vp9_avg_8tap_smooth_8h_10bpp_neon:       327.0     314.0
vp9_avg_8tap_smooth_8hv_10bpp_neon:      918.7     865.4
vp9_avg_8tap_smooth_8v_10bpp_neon:       330.0     300.2
vp9_avg_8tap_smooth_16h_10bpp_neon:     1187.5    1155.5
vp9_avg_8tap_smooth_16hv_10bpp_neon:    2663.1    2591.0
vp9_avg_8tap_smooth_16v_10bpp_neon:     1107.4    1078.3
vp9_avg_8tap_smooth_64h_10bpp_neon:    17754.6   17454.7
vp9_avg_8tap_smooth_64hv_10bpp_neon:   33285.2   33001.5
vp9_avg_8tap_smooth_64v_10bpp_neon:    16066.9   16048.6
vp9_put4_10bpp_neon:                      25.5      21.7
vp9_put8_10bpp_neon:                      56.0      52.0
vp9_put16_10bpp_neon/armv8:              183.0     163.1
vp9_put32_10bpp_neon/armv8:              678.6     563.1
vp9_put64_10bpp_neon/armv8:             2679.9    2195.8
vp9_put_8tap_smooth_4h_10bpp_neon:       120.0     118.0
vp9_put_8tap_smooth_4hv_10bpp_neon:      435.2     435.0
vp9_put_8tap_smooth_4v_10bpp_neon:       107.0      98.2
vp9_put_8tap_smooth_8h_10bpp_neon:       303.0     290.0
vp9_put_8tap_smooth_8hv_10bpp_neon:      893.7     828.7
vp9_put_8tap_smooth_8v_10bpp_neon:       305.5     263.5
vp9_put_8tap_smooth_16h_10bpp_neon:     1089.1    1059.2
vp9_put_8tap_smooth_16hv_10bpp_neon:    2578.8    2452.4
vp9_put_8tap_smooth_16v_10bpp_neon:     1009.5     933.5
vp9_put_8tap_smooth_64h_10bpp_neon:    16223.4   15918.6
vp9_put_8tap_smooth_64hv_10bpp_neon:   32153.0   31016.2
vp9_put_8tap_smooth_64v_10bpp_neon:    14516.5   13748.1

These are generally about as fast as the corresponding ARM
routines on the same CPU (at least on the A53), in most cases
marginally faster.

The speedup vs C code is around 4-9x.
Signed-off-by: Martin Storsjö <martin@martin.st>