Adds high bitdepth transform functions and tests

Adds high bitdepth transform functions and tests

Adds various high bitdepth transform functions and tests.
Much of the changes are related to using typedefs tran_low_t
and tran_high_t for the final transform cofficients and intermediate
stages of the transform computation respectively rather than fixed
types int16_t/int. When vp9_highbitdepth configure flag is off,
these map tp int16_t/int32_t, but when the flag is on, they map
to int32_t/int64_t to make space for needed extra precision.

Change-Id: I3c56de79e15b904d6f655b62ffae170729befdd8