usb: dwc3-msm: Reduce usage of usb power_supply

On platforms with multiple USB controller instances, usually only
one is associated with the charger and the single instance of the
"usb" power_supply. Thus the non-charging instances do not need
to access it.

Even in that case it is now only useful for setting max current
based on enumeration in device mode. It is no longer required to
query for PROP_PRESENT during probe so getting of the usb_psy can
be removed there as well. Finally remove setting of
PROP_BOOST_CURRENT which is also no longer used.

Change-Id: I6f393105b65c6580a92e3161d16b1e2dce11a37d
Signed-off-by: Jack Pham <jackp@codeaurora.org>