media: vsp1: Add missing export.h

As reported by the Kernel Test Robot, the newly merged vspx driver
exports a few symbols but doesn't include the export.h header.

While at it, include the header file in vsp1_drm.c which exports
symbols as well.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202506181950.r9PRdV59-lkp@intel.com/


Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/20250618-vspx-include-export-v1-1-95a2da4ec465@ideasonboard.com


Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>