ARM: dts: zynq: replace gpio-key,wakeup with wakeup-source property

Most of the legacy "gpio-key,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 700a38b2

 ("Input: gpio_keys -
switch to using generic device properties")

Cc: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>