Add 4-positon dip switch GPIO

Add the 4-positon dip switch to the device tree by
enabling the GPIO pins and adding a device node.

Signed-off-by: Jeff Horn <jhorn@reachtech.com>
Initial driver support for 4-position dip switch

This adds driveer support and a /sys/kernel/dipswitch
interface.

Signed-off-by: Jeff Horn <jhorn@reachtech.com>