sfc: Expose flash region storing boot code as MTD The boot code that appears as a PCI expansion ROM on the SFC4000 is stored in flash. Expose this as a standard MTD device to allow for in-place upgrades. Signed-off-by: Ben Hutchings <bhutchings@solarflare.com> Signed-off-by: Jeff Garzik <jgarzik@redhat.com>