ARM: shmobile: Add GPIO keys to Koelsch DTS

The Koelsh reference device tree is going away, copy the missing GPIO
keys device node to the Koeslch device tree file.

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