power: supply: Add support to report QC3+ adapter power rating

Report the QC3+ adapter power-rating via "power_now" in the usb
power-supply class.

Change-Id: I0d0e9a3e9d2f5d57f5e8696dea8f4e17a8f2df5f
Signed-off-by: Ashish Chavan <ashichav@codeaurora.org>