ARM: shmobile: mackerel: Register IRQ pinctrl mapping for SDHI0

Replace the GPIO-based SDHI0 IRQ pinmux configuration by a pinctrl
mapping.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>