drm/amd/display: Exit idle optimizations before accessing PHY

[why & how]
By default, DCN HW is in idle optimized state which does not allow access
to PHY registers. If BIOS powers up the DCN, it is fine because they will
power up everything. Only exit idle optimized state when not taking control
from VBIOS.

Fixes: be704e5e ("Revert "drm/amd/display: Exit idle optimizations before attempt to access PHY"")
Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Signed-off-by: Ovidiu Bunea <Ovidiu.Bunea@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>