drm/amd/display: Fix IPS handshake for idle optimizations

drm/amd/display: Fix IPS handshake for idle optimizations

[Why]
Intermittent reboot hangs are observed introduced by
"Improve x86 and dmub ips handshake".

[How]
Bring back the commit but fix the polling.

Avoid hanging in place forever by bounding the delay and ensure that
we still message DMCUB on IPS2 exit to notify driver idle has been
cleared.

Reviewed-by: Duncan Ma <duncan.ma@amd.com>
Reviewed-by: Jun Lei <jun.lei@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>