Add a regulator consumer driver for rfkill to enable controlling radio
transmitters connected to voltage regulators using the regulator
framework.

A new "vrfkill" virtual supply is provided to use in platform code.
Signed-off-by: NGuiming Zhuo <gmzhuo@gmail.com>
Signed-off-by: NAntonio Ospite <ospite@studenti.unina.it>
Reviewed-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>