net: rfkill: convert net/rfkill/* to use module_platform_driver()

This patch converts the drivers in net/rfkill/* to use the
module_platform_driver() macro which makes the code smaller and a bit
simpler.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: "John W. Linville" <linville@tuxdriver.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Antonio Ospite <ospite@studenti.unina.it>
Cc: Rhyland Klein <rklein@nvidia.com>
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Rhyland Klein <rklein@nvidia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>