BD-rate performance improvement (on top of ext-intra):
derflr  0.22%
hevclr  0.36%
hevcmr  0.48%
hevchr  0.37%
stdhd   0.19%

Average speed impact on some derf clips is about 40% slower (on
top of ext-intra). Speed improvment is a to-do.

Change-Id: I8fe3fe8c5e4f60d0462778adbcc15c84dfbe7a25