sh: sh7723 / ap325rxa enable SDIO IRQs

This patch enables the interrupt generation for SDIO IRQs
of the sdhi controllers of the SoC. To make sure SDIO IRQs
are used announce the MMC_CAP_SDIO_IRQ capability
on ap325rxa.

Signed-off-by: Arnd Hannemann <arnd@arndnet.de>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>