ARM: shmobile: r8a7740: Add pin control device to device tree

Add a pfc node to the r8a7740 device tree and remove manual pinmux
initialization from the corresponding board files.

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