This commit factors out common macro definitions from the forward
and inverse transform implementations into vpx_dsp. It removes
the duplicate macro definitions from encoder and decoder folders.
Change-Id: I92301acbd3317075e9c5f03328a25abb123bca78
Updated sources according to improved version of common MSA macros.
Enabled idct MSA hooks and tests.
Overall, this is just upgrading the code with styling changes.
Change-Id: I1f488ab2c741f6c622b7a855388a202168082209