drm/amd/display: Power eDP panel back ON before link training retry

[why]
When link training failures occur for eDP, dp_disable_link_phy
is called which powers OFF eDP panel. After link training retry
delay, the next retry begins by calling dp_enable_link_phy
which does not issue a correspnding eDP panel power ON, leaving
panel powered OFF which leads to display OFF/dark.

[how]
Power ON eDP before next link training retry.

Signed-off-by: Ashley Thomas <Ashley.Thomas2@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>