ARM: dts: am335x/am57xx: replace gpio-key,wakeup with wakeup-source property

Commit 3efda001 ("ARM: dts: am335x: replace gpio-key,wakeup with
wakeup-source property") replaces all the legacy "gpio-key,wakeup" with
the unified  "wakeup-source" property to prevent any further copy-paste
duplication.

However couple of use of these legacy property sneaked in during the
merge window. This patch replaces them too.

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