drm/i915/kbl: Add KBL GT2 sku

Adding a missing GT2 sku discovered off hardware.
Signed-off-by: NMatt Atwood <matthew.s.atwood@intel.com>
Reviewed-by: NClint Taylor <clinton.a.taylor@intel.com>
Signed-off-by: NRodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1524522483-19987-1-git-send-email-matthew.s.atwood@intel.com

include/drm/i915_pciids.h

@@ -349,6 +349,7 @@
 #define INTEL_KBL_GT2_IDS(info)	\
 	INTEL_VGA_DEVICE(0x5916, info), /* ULT GT2 */ \
 	INTEL_VGA_DEVICE(0x5917, info), /* Mobile GT2 */ \
+	INTEL_VGA_DEVICE(0x591C, info), /* ULX GT2 */ \
 	INTEL_VGA_DEVICE(0x5921, info), /* ULT GT2F */ \
 	INTEL_VGA_DEVICE(0x591E, info), /* ULX GT2 */ \
 	INTEL_VGA_DEVICE(0x5912, info), /* DT  GT2 */ \