qcom: smb138x-charger: Add support for setting parallel mode

More than one parallel configurations between PMI8998 and SMB138x are
supported. Update the parallel mode from DT.

Change-Id: I07c30e8d4d860acaf24dd5d0608dca6ba3e65559
Signed-off-by: Harry Yang <harryy@codeaurora.org>
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>