drm/amd/display: fix IPX enablement

We need to re-enable idle power optimizations after entering PSR. Since,
we get kicked out of idle power optimizations before entering PSR
(entering PSR requires us to write to DCN registers, which isn't allowed
while we are in IPS).

Fixes: a9b1a4f6 ("drm/amd/display: Add more checks for exiting idle in DC")
Tested-by: Mark Broadworth <mark.broadworth@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>