drm: Kbuild: add omap_drm.h to the installed headers

The header defines the userspace API exported by the omapdrm driver,
install it to make the definitions available to userpace.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

include/uapi/drm/Kbuild

@@ -9,6 +9,7 @@ header-y += i810_drm.h
 header-y += i915_drm.h
 header-y += mga_drm.h
 header-y += nouveau_drm.h
+header-y += omap_drm.h
 header-y += qxl_drm.h
 header-y += r128_drm.h
 header-y += radeon_drm.h