drm/i915: Skip SINK_COUNT read on CH7511

CH7511 doesn't update SINK_COUNT properly so in order to detect
the device as connected we have to ignore SINK_COUNT.

In order to have access to the quirk list early enough we
must move the drm_dp_read_desc() call to happen earlier.
We can also skip re-reading this on eDP since we know it
won't change.

Cc: David S. <david@majinbuu.com>
Cc: Peteris Rudzusiks <peteris.rudzusiks@gmail.com>
Tested-by: Peteris Rudzusiks <peteris.rudzusiks@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105406


Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528140650.19230-2-ville.syrjala@linux.intel.com
Acked-by: Jani Nikula <jani.nikula@intel.com> #irc