drm/amd/display: Read LTTPR caps first on hotplug

[WHY]
A new SCR for the DP2.0 spec requires that LTTPR caps be the first thing
read from DPCD upon hotplug.

Signed-off-by: Wesley Chalmers <Wesley.Chalmers@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>