drm/amd/display: do not read link setting if edp not connected

[Why]
Previously assume eDP sink present if connector present. Do not
need to enforce this restriction. Fix issue where driver attempt
to read link setting even though no edp connected.

{How]
Only read link setting after reading connection status.

Signed-off-by: Eric Yang <Eric.Yang2@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>