drm/amd/display: Check hw_init state when determining if DMCUB is initialized

[Why]
CW2 may already be programmed when coming back from S4. In this case
we want to unconditionally replace whatever DMCUB version is currently
enabled with the latest.

[How]
Check the hw_init flag to know whether or not we've previously executed
the initliazed routine.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>