Use sharp filter for alter reference frame generation

This commit uses 12-tap sharp filter to generate alter reference
frame. It improves the compression performance by
derf    0.45%
hevcmr  0.35%
stdhd   0.79%

No encoding time change is observed.

Change-Id: Ia5dc26d5aae6b9b0cb782e5a28dc5066eeeb2ec8
3 files changed