arm64: dts: zynqmp: 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.

This patch replaces the legacy properties with the unified
"wakeup-source" property introduced by:
"Input: gpio_keys - switch to using generic device properties"
(sha1: 700a38b2)

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>