drm/amd/display: Force delay after DP receive power up

[Why]
Some sprcified monitor scalar cannot recognize timing
change on demand. Once the link phy disable and enable
during a short period then the Sink protection mechanism
could keep the screen in blank and cannot be recoverred.

[How]
To add 100ms delay between enable link phy and link training.

Signed-off-by: Martin Tsai <martin.tsai@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>