Keep the idct32 coefficients in narrow form in q6-q7, and idct16
coefficients in lengthened 32 bit form in q0-q3. Avoid clobbering
q0-q3 in the pass1 function, and squeeze the idct16 coefficients
into q0-q1 in the pass2 function to avoid reloading them.
The idct16 coefficients are clobbered and reloaded within idct32_odd
though, since that turns out to be faster than narrowing them and
swapping them into q6-q7.
Before: Cortex A7 A8 A9 A53
vp9_inv_dct_dct_32x32_sub4_add_10_neon: 22653.8 18268.4 19598.0 14079.0
vp9_inv_dct_dct_32x32_sub32_add_10_neon: 37699.0 38665.2 32542.3 24472.2
After:
vp9_inv_dct_dct_32x32_sub4_add_10_neon: 22270.8 18159.3 19531.0 13865.0
vp9_inv_dct_dct_32x32_sub32_add_10_neon: 37523.3 37731.6 32181.7 24071.2
Signed-off-by: Martin Storsjö <martin@martin.st>
