ARM: dts: omap: replace legacy *,wakeup property with wakeup-source

Though the keyboard and other driver will continue to support the legacy
"gpio-key,wakeup", "linux,wakeup" boolean property to enable the wakeup
source, "wakeup-source" is the new standard binding.

This patch replaces all the legacy wakeup properties with the unified
"wakeup-source" property in order to avoid any futher copy-paste
duplication.

Cc: "Benoît Cousson" <bcousson@baylibre.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: linux-omap@vger.kernel.org
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>