ARM: dts: am437x: replace linux,wakeup with wakeup-source property

Most of the legacy "linux,wakeup" boolean property is already replaced
with "wakeup-source". However few occurrences of old property has popped
up again, probably from the remnants in downstream trees.

Replace the legacy properties with the unified "wakeup-source" property
introduced in the commit aeda5003 ("Input: matrix_keypad - change
name of wakeup property to "wakeup-source"")

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>