drm/amd/display: Change dmcu init sequence for dmcub loading dmcu FW.

drm/amd/display: Change dmcu init sequence for dmcub loading dmcu FW.

[Why]
DMCU isn't intiliazed properly by dmcub loading due to dmcub initialize
sequence.

[How]
Change dmcu init sequece to meet dmcub initilize.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Hersen Wu <hersenxs.wu@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>