Tweaks to mediaformatshaper

-- parameterize the % boost if QP is desired but not present
-- parameterize the upper bounds for where shaping is phased out
-- tuning default bits-per-pixel for AVC

Bug: 183211971
Test: video quality test scripts
Change-Id: I2e83c574e766606c50d7ed5dc26c49ba92ecb2a4