mfd: AS3722: Add dt node properties for system power controller

ams AS3722 device supports the power off by turning off its all rails.

Add dt node properties to enable this functionality on this device.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>