Add av1_inverse_transform_block

Move most of the code of inverse_transform_block to
av1_inverse_transform_block such that encoder can use the
function as well.

Use av1_inverse_transform_block in av1_encoder_block_intra.
This will make the code cleaner.

Change-Id: I84dbeef2c65e252910606dbea446ce43165d504c
4 files changed