drm/amd/display: exit PSR during detection

[Why]
If 48mhz refclk is turned off during PSR, we will have issue doing
link training during detection.

[How]
Get out of PSR before detection

Signed-off-by: Eric Yang <Eric.Yang2@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>