Add support to program the DCN2 MMHUBBUB (Multimedia HUB interface)

HW Blocks:

 +--------++------+       +----------+
 | HUBBUB || HUBP |  <--  | MMHUBBUB |
 +--------++------+       +----------+
        |
        v
    +--------+
    |  DPP   |
    +--------+
        |
        v
    +--------+
    |  MPC   |
    +--------+
        |
        v
    +-------+
    |  OPP  |
    +-------+
        |
        v
    +--------+
    |  OPTC  |
    +--------+
        |
        v
    +--------+       +--------+
    |  DIO   |       |  DCCG  |
    +--------+       +--------+
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>