Keyboard driver for GPIO buttons(gpio-keys) checks for the legacy
"gpio-key,wakeup" boolean property to enable gpio buttons as wakeup
source.

Few dts files assign value "1" to gpio-key,wakeup and in one instance a
value "0" is assigned probably assuming it won't be enabled as a wakeup
source. Since the presence of the boolean property indicates it is
enabled, value of "0" have no value.

This patch replaces the legacy "gpio-key,wakeup" with the unified
"wakeup-source" property which inturn fixes the above mentioned issue.
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>