FMC: add a software carrier driver

This fake carrier is designed to help FMC users understand how a
carrier driver works, and to experiment the behaviour with EEPROM
reprogramming (with a mezzanine driver commited later). This carrier
can register up to 4 (fake) mezzanines.

We have real carriers (both on PCI-E and VME), but they are bigger
things and are not part of this submission.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
Acked-by: Juan David Gonzalez Cobas <dcobas@cern.ch>
Acked-by: Emilio G. Cota <cota@braap.org>
Acked-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>