drivers/fsi: Add empty master scan

When a new fsi master is added, we will need to scan its links, and
slaves attached to those links. This change introduces a little shell to
iterate the links, which we will populate with the actual slave scan in
a later change.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Chris Bostic <cbostic@linux.vnet.ibm.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>