/i915/dp: Probe branch/sink OUIs

v2: Do the eDP vdd dance of simply not probing the OUI on eDP panels
as suggested by Chris Wilson.

v3: Fix up the error path fail - I suck.

Cc: Adam Jackson <ajax@redhat.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50808
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Bugreport: http://permalink.gmane.org/gmane.comp.video.dri.devel/69695
Tested-by: Yang Guang <guang.a.yang@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
ðpNÖ“,x