Removed bmi copy to/from BLOCKD

for SPLITMV and B_PRED modes.  Modified code to use the bmi
found in mode_info_context instead of BLOCKD.  On the decode
side, the uvmvs are calculated only when required, instead of
every macroblock.  This is WIP. (bmi should eventually be
removed from BLOCKD)
Small performance gains noticed for RT encodes and decodes.(VGA)

Change-Id: I2ed7f0fd5ca733655df684aa82da575c77a973e7