Add OLPC XO-1 rfkill driver

Add a software rfkill switch for the WLAN interface in the OLPC XO-1
laptop. It uses the OLPC embedded controller to cut/restore power to
the Marvell WLAN chip on the motherboard.

Signed-off-by: Daniel Drake <dsd@laptop.org>
Signed-off-by: Matthew Garrett <mjg@redhat.com>