power: smb350: add support for smb350 battery charger

The SMB350 switched-mode based external charger supports
stack-cell battery charging.
The driver controls charger-enable and charger-suspend/resume
via the device EN and SUSP pins.
The driver reports the charger status via the power supply framework.
IRQ is triggered by the device STAT pin upon status change.

Change-Id: Iea5706421b252c586d9c79d9688e7899f12f04a8
Signed-off-by: Amir Samuelov <amirs@codeaurora.org>