drm/i915: refactor VBT validation
Make the validation function a boolean operating on a buffer of given
size, removing the extra pointer dances.
Move the OpRegion based VBT validation to intel_opregion_setup(), only
initializing opregion->vbt if it's valid.
v2: move logging about valid VBT to opregion setup too (Ville)
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1450178175-27420-1-git-send-email-jani.nikula@intel.com