pcmcia: remove pccard_sysfs_interface warnings

Make the PCMCIA core stop using class_interface to hide socket attribute
registration.  This removes the associated section mismatch warnings, and
helps get to the point where that mechanism can finally be removed.

Simplify that attribute registration by using an attribute_group.
This is a net shrink in object size.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>