qcom-charger: smb138x: Add MODEL_NAME property for parallel

Currently there is no easy way to detect the device name based on
the bus or device sysfs properties.

Implement MODEL_NAME property to identify the parallel charger.

Change-Id: I8134b415a2b36e249b098f4b61d4dd8415008cfa
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>