irqdomain: Added domain bus token DOMAIN_BUS_FSL_MC_MSI

Since an FSL-MC bus is a new bus type that is neither PCI nor
PLATFORM, we need a new domain bus token to disambiguate the
IRQ domain for FSL-MC MSIs.

Signed-off-by: J. German Rivera <German.Rivera@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>