Add a new registration function to register the PCMCIA 16-bit subsystem
(ds a.k.a. pcmcia) with the PCMICA core (cs a.k.a. pcmcia_core).

As send_event is only called with skt->sem held, we can use that to safeguard
skt->callback(), too. Note that the class_device_register() call by pccardd()
is done _before_ skt->sem() is held, and the pcmcia_socket_register() doesn't
hold skt->sem() as well, so there is no chance for a deadlock.
Signed-off-by: Dominik Brodowski <linux@brodo.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>