Turn on adaptive pred filter scheme for sub8x8 below 720p

Turn on adaptive pred filter scheme for sub8x8 below 720p

For sequences of resolution below 720p, the encoder will check
intra prediction modes and inter prediction modes from LAST_FRAME.
This commit turns on adaptive prediction filter scheme for sub8x8
blocks, where inter prediction modes are enabled. For the test
sequence bus at CIF, the speed 2 runtime goes down from 17879 ms
to 16783 ms, i.e., 6% speed up. The compression performance of
derf set is down by -0.128%.

Change-Id: I01d5321a5ceab4e0666ac5be56c52d896c7a8d45