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

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

Though the keyboard driver for GPIO buttons(gpio-keys) will continue to
check for/support the legacy "gpio-key,wakeup" boolean property to
enable gpio buttons as wakeup source, "wakeup-source" is the new
standard binding.

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

Cc: Michal Simek <[email protected]>
Cc: "Sören Brinkmann" <[email protected]>
Signed-off-by: Sudeep Holla <[email protected]>
Signed-off-by: Michal Simek <[email protected]>