drm/amd/display: Reduce CPU busy-waiting for long delays

[WHY]
udelay should not be used for long waits since it keeps CPU active,
wasting power.

[HOW]
Use fsleep where acceptable to allow CPU cores to be parked by the scheduler.

Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Aric Cyr <aric.cyr@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>