arm64: dts: apm: Update GPIO to control power-off on X-Gene v2 platforms

This patch updates gpio-keys node that supports power-off for
X-Gene v2 Merlin board to adapt with new changes in xgene-gpio-sb
driver (to support configuring some GPIO pins as interrupt pins).

Signed-off-by: Quan Nguyen <qnguyen@apm.com>
Signed-off-by: Duc Dang <dhdang@apm.com>