mmc: sh_mobile_sdhi: enable SDIO IRQs for RCar Gen3

Tested on a Salvator-X board with a Spectec SDW-823 WLAN card.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>