power: smb350: improve smb350 driver

Improve the driver by implementing following changes
* rename suspend gpio to shutdown gpio - that is the correct name of
  the pin.
* passing the stat gpio and then mapping it to irq is
  unnecessary. Instead pass the interrupt information via device tree
  node.
* use threaded interrupts instead of a hard context handler invoking
  a workqueue.
* Create battery power supply and reorganize power supply properties
 between battery and dc.
* enable charging by default.
* refactor the probe function to separately
** parse dt files
** intialize hardware
** register power supply structures
** debugfs file creation

Change-Id: I825a20c1ce8f8f81265bfbe88f4822e22312e954
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>