power: smb1390: enable device suspend

SMB1390 driver holds a wakeup source to avoid I2C transaction failure
during system suspend and thus causing high current consumption. Fix
I2C failures during suspend by reporting cached chip state during suspend
thus avoiding any I2C transaction during suspend.

Change-Id: I800dba679c9747ce1be26c0e3f6fe625dee82a46
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>