staging: fsl-mc: Added generic MSI support for FSL-MC devices

Created an MSI domain for the fsl-mc bus-- including functions
to create a domain, find a domain, alloc/free domain irqs, and
bus specific overrides for domain and irq_chip ops.

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