checkasm benchmarks on 1.5 GHz Cortex-A72 are as follows.

idctdsp.add_pixels_clamped_c: 313.3
idctdsp.add_pixels_clamped_neon: 24.3
idctdsp.put_pixels_clamped_c: 220.3
idctdsp.put_pixels_clamped_neon: 15.5
idctdsp.put_signed_pixels_clamped_c: 210.5
idctdsp.put_signed_pixels_clamped_neon: 19.5
Signed-off-by: Ben Avison <bavison@riscosopen.org>
Signed-off-by: Martin Storsjö <martin@martin.st>