net: rfkill: add generic gpio rfkill driver

This adds a new generic gpio rfkill driver to support rfkill switches
which are controlled by gpios. The driver also supports passing in
data about the clock for the radio, so that when rfkill is blocking,
it can disable the clock.

This driver assumes platform data is passed from the board files to
configure it for specific devices.

Original-patch-by: Anantha Idapalapati <aidapalapati@nvidia.com>
Signed-off-by: Rhyland Klein <rklein@nvidia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>