Driver Core: block: add nodename support for block drivers.

This adds support for block drivers to report their requested nodename
to userspace.  It also updates a number of block drivers to provide the
needed subdirectory and device name to be used for them.

Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Jan Blunck <jblunck@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>