drm/amd/display: remove early return from dm_late_init

[Why]
ABM feature initialization was not executed due to early return.

dm_late_init() had an early return in case if DMCU is not used.
With the implementation of ABM on DMUB, DMCU can be disabled
but ABM still needs to be initialized.

[How]
Remove verification for DMCU from the top of the function.
The existing logic will handle the case when DMCU is not used.

Signed-off-by: Roman Li <roman.li@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>