drm/i915: Add I2C and DP-AUX char devices to debug kconfig

drm/i915: Add I2C and DP-AUX char devices to debug kconfig

These char devices exposing the driver's I2C and DP-AUX adapters for
user space tools are useful to debug display output related issues.
Enable them with the rest of additional driver debug options.

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1480696541-13697-1-git-send-email-imre.deak@intel.com