ngw100: export J15 through sysfs

The NGW100 board has jumper J15 (near the reset button) which
is unused.  This patch exports it through the GPIO sysfs support
(as /sys/class/gpio/gpio62/value) so that it's easily queried
by boot scripts or whatever might want to know if the jumper
has been installed (value = 0) or not (value = 1, "default").

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
[haavard.skinnemoen@atmel.com: add missing include]
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>