Enable recursive partition selection for non-RD coding mode

This commit enables a recursive partition type search for non-RD
mode decisions. It allows the encoder to choose variable block
sizes in a 64x64 block based on rate-distortion modeling.

It improves speed -6 coding efficiency for rtc set by 2.4%. Most
of the gains come from 32-40dB range, where many sequences gain
about 5% to 20%. Local tests suggest there is no speed change.

Change-Id: I06300016e500a21652812b7b3b081db39a783d66