mfd: sh_mobile_sdhi: activate SDIO IRQ for tmio_mmc

The SDHI Controller on SH-Mobile SoCs supports SDIO IRQ signalling.
This patch advertises this fact to the tmio_mmc driver.

Signed-off-by: Arnd Hannemann <arnd@arndnet.de>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>