power_supply: add change the scope property

The scope property indicates the operating mode of the system. This
property could be used to switch to and from usb host mode.

Add a helper api to update this property.

CRs-Fixed: 373365
Change-Id: I5fb57f7b1075276ba90b0f7e0a44626e07ee196f
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>