Use luma pixel coordinates in TU coding functions
Use luma pixel coordinates in TU coding functions

Changes functions encode_transform_unit and encode_transform_coeff to
take coordinate arguments in units of luma pixels instead of 4 px
blocks. This should make the code easier to understand.

ultravideo/kvazaar,ultravideo/kvazaar,ultravideo/kvazaar,ultravideo/kvazaar,ultravideo/kvazaar