smb138x: support ship mode

Provide means to set ship mode on smb138x charger. While in parallel
charger mode make the main charger set ship mode on smb138x before
calling ship mode on itself.

Change-Id: I9b96b425829520d95632aa32d2297940cca5e254
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>