sh-pfc: r8a7740: Declare missing INTC function

When adding the INTC pin groups the INTC function hasn't been added to
the functions list. Fix it.

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