[PCMCIA] core socket sysfs support, export card type

[PCMCIA] core socket sysfs support, export card type

Patch from Dominik Brodowski

Add a first socket-related sysfs entry; and to keep things ordered,
do so in a new file drivers/pcmcia/socket_sysfs.c. To keep things
easy, all files will be present all the time, even if no card is in
the socket at a specific moment -- however, accessing the file will
result in -ENODEV then, so that

# cat /sys/class/pcmcia_socket/pcmcia_socket1/card_type

will cause an error message like

"cat: card_type: No such device"

which is quite self-explanatory.

The attribute "card_type" will return either "16-bit" or "32-bit",
depending on whether the PCCard is a 16-bit PCMCIA card or a 32-bit
CardBus card. The result "invalid" should not happen, and if it
happens, something strange is going on.