Change in rddiv parameter to make it a power of 2

Change in rddiv parameter to make it a power of 2

Converts the constant rddiv parameter to 128 (from 100) and
implements RDCOST with bit-shift rather than multiplication.
Other parameters are also adjusted to roughly keep the same
balance between Rate and Distortion.

There is a slight speed-up of about 0.5-1% (at speed 0) as
testted on football_cif.

There is a slight change in performance due to small change
in the parameters.
derfraw300: +0.033%
stdhdraw250; +0.102%

Change-Id: I70ac69f58fa71c83108f68fe41796cd19d1fc760