staging: ipack: only build on platforms that provide ioread/iowrite.

Do so by depending on HAS_IOMEM.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Jens Taprogge <jens.taprogge@taprogge.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>