Code class0 using aom_read() / aom_write().

The av1_mv_class0_tree is a balanced tree with two leafs and can
 simply be coded as a boolean with probability class0[0].
If CLASS0_SIZE is ever changed from 1, this change will need to be
 reverted.

Change-Id: If294dac825a5f945371092c74aa8e3f84cd962b6
2 files changed