drm/amd/display: fix hotplug during display off

[why]
HPD is not suppressed when we lower
clocks on renoir. B/c of this we do link
training when the 48mhz refclk is off, which
will cause ASIC hang.

[how]
Exit optimized power state for detection purpose.

Signed-off-by: Joseph Gravenor <joseph.gravenor@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>