Enable using fast HEX search in non-rd pick mode

Added fast HEX search while doing non-rd partition picking to
speed up the encoder.

Borg test(speed 7) on rtc set showed 1.8% overall PSNR loss.
Encoder speedup was 5% - 15% for different rtc clips.

Change-Id: I9c83026eabc70b69fcc747c90369ec60bfa3ca24