power: charger: get the current information from usb-otg

usb_otg is able to know what kind of charger is connected like as
USB, TA and  Slimport. And we can decide the max charging current
by cable type. pm8921-charger is able to use this information.

And unplug_check_worker has some problem. Wrong charging current
might set as 100mA even thought USB charger can be set by max 500mA.
It cause very slow charging.

msg_otg didn't use power supply api properly due to not supported
some POWER_SUPPLY_PROPs in pm8921-charger.c. It's also fixed.

Change-Id: I86661fbe38e3db5522caab6ff316c0100f87fe0d