parisc: parisc-agp requires SBA IOMMU driver

Add a dependency to the SBA IOMMU driver to avoid:
ERROR: modpost: "sba_list" [drivers/char/agp/parisc-agp.ko] undefined!

Reported-by: kernel test robot <lkp@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Helge Deller <deller@gmx.de>