Factor out the functionality for adding and removing a single
socket, thereby allowing SoCs to individually register each
socket.  The advantage of this approach is that SoCs can then
extend soc_pcmcia_socket as they wish.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>