drm/i915/dp: Print only sink or branch specific OUI based on dev type

There are two separate sets of DPCD registers for the DP OUI - as well as
for the device ID and HW/SW revision - based on whether the given DP
device is a branch or a sink. Currently we print both branch and sink
OUIs, for consistency print only the one that corresponds to the
probed device.

v2:
- Split out this change into a separate patch. (Jani)

Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1477326811-30431-4-git-send-email-imre.deak@intel.com