Apply finer quantizer to partition search frames in non-RD flow

This commit optimizes the bit allocation for the non-RD coding flow.
It applies slightly better quantizer to the frames, where all blocks
run a non-RD partition search. Such frames typically have better
rate-distortion trade off, thus improving the reconstruction quality
for next few frames reference at reasonably low increment in rate
cost.

The coding performance for rtc set at speed -5 with error-resilient
tuned on and rate control set as cbr is improved by 19.58%. It improved
the coding speed by about 10% for a portion of local test clips.

Change-Id: I9d56696cd4359dc8136ca10aff10fff05aaa2686