[PCMCIA] "driver services" socket add/remove abstraction

Previously, "Driver Services" could only be called when the socket
drivers were initialized earlier. This caused an awful lot of
problems, especially when modprobe tried to load ds.ko and a pcmcia
card driver at once.

As all socket devices are registered with the driver model core as
being of "class_type pcmcia_socket_class", we can take use of that and
register them with "Driver Services" upon detection or upon
module loading of ds.c.

Also, the "I-need-two-initcalls-in-a-module"-tweak can go away.

Unfortunately, this patch reportedly breaks some RedHat pcmcia init
scritps - they relied on the failed loading of ds.c to detect that no
socket driver was loaded previously. To properly detect this, you
should take a look at the /sys/class/pcmcia_socket/devices directory.