Reduced the size of MB_MODE_INFO

Moved partition_bmi and partition_count out of MB_MODE_INFO and
placed into MACROBLOCK.  Also reduced the size of other members
of the MB_MODE_INFO struct.  For 1080p, the memory was reduced
by 1,209,516 bytes.  The decoder performance appeared to improve
by 3% for the clip used.
Note:  The main goal for this change is to improve the decoder
performance.  The encoder will be revisited at a later date for
further structure cleanup.

Change-Id: I4733621292ee9cc3fffa4046cb3fd4d99bd14613