drm/amd/display: Spin for DMCUB PHY init in DC

[Why]
DCN will hang if we access registers before PHY init is done.

So we need to spin or abort.

[How]
On hardware with DMCUB running and working we shouldn't time out
waiting for this to finish and we shouldn't hit the spin cycle.

If there's no hardware support then we should exit out of the function
early assuming that PHY init was already done elsewhere.

If we hit the timeout then there's likely a bug in firmware or software
and we need to debug - add errors and asserts as appropriate.

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