Removes conditional statements from band getting

Implements scan order to band map with arrays in both the encoder
and decoder to remove conditional statements.

Encoding seems to be about 1% faster at speed 0, tested on football.
Decoding seems to be about 0.5-1% faster on a set of 25 videos.

Change-Id: Idb233ca0b9e0efd790e30880642e8717e1c5c8dd