Make sb intra rd search consistent with encoding

This commit makes operations of the superblock intra coding rate
distortion optimization consistent with those used in the encoding
process. Given the test prediction mode and transform size, the rd
optimizer encodes and reconstructs each transformed block of the
superblock consecutively, then computes the total rate-distortion
costs accosicated with the current superblock to select the coding
decisions.

It achieves coding performance gains:
derf 0.353%
yt   1.111%

Change-Id: I0da2eb7a71361dfb8c1384927fc536b0c2790d07