ARM: dts: msm: Enable charging and serial_2 USB function for sdx20

Charging is standard HID function and serial_2 function is
second instance of serial/DUN function to enable in second
configuration. It allows serial (2) function to exist in
second configuration with existing serial_func present in
first configuration.

Change-Id: I3c7f60de444b651bc90daabc0799d881cea3e690
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>