drm/i915/dsi: skip gpio element execution when not supported

drm/i915/dsi: skip gpio element execution when not supported

Skip v3 gpio element because the support is not there, and skip gpio
element on non-vlv because the sideband code is vlv specific.

v2: the gpio stuff is currently only supported on vlv (Ville)

Cc: drm-intel-fixes@lists.freedesktop.org
Fixes: 596a24d155b1 ("drm/i915/bios: add support for MIPI sequence block v3")
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/1454604767-2440-1-git-send-email-jani.nikula@intel.com