Implements some of the helper functions more efficiently with
lookups rathers than branches. Modeling function is consolidated
to reduce some computations.
Also merged the two enums BLOCK_SIZE_TYPES and BlockSize into
one because there is no need to keep them separate (even though
the semantics are a little different).
No bitstream or output change.
About 0.5% speedup
Change-Id: I7d71a66e8031ddb340744dc493f22976052b8f9f
94c481f9f1