Add programming of the DCCG (Display Controller Clock Generator) block:

HW Blocks:

    +--------+
    |  DCCG  |
    +--------+
Acked-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>