ARM: dts: Replace legacy *,wakeup property with wakeup-source for exynos boards

Though the keyboard and other driver will continue to support the legacy
"gpio-key,wakeup", "linux-keypad,wakeup" boolean property to enable the
wakeup source, "wakeup-source" is the new standard binding.

This patch replaces all the legacy wakeup properties with the unified
"wakeup-source" property in order to avoid any further copy-paste
duplication.

Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>