drm/amd/display: Exit idle optimizations before attempt to access PHY

[Why & How]
DMUB may hang when powering down pixel clocks due to no dprefclk.

It is fixed by exiting idle optimization before the attempt to access PHY.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Leo Chen <sancchen@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>