power: pm8921 and ltc4088-charger: add pm_power_set_property

Add pm_power_set_property_usb API to support the power
supply framework APIs which allow changing the type of
a given power supply.

This is required to avoid the use of PMIC specific APIs
in the USB driver and encourage the use of the power
supply framework.

Change-Id: Ifba2bd1248e8bb47a0700dec4d321d32db4f2066
Signed-off-by: David Keitel <dkeitel@codeaurora.org>