staging: fsl-mc: move irq domain creation prototype to public header

fsl_mc_msi_create_irq_domain() will is used from the irqchip glue code
so it needs to be in the public headers.

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>