genirq/msi: Split msi_create_irq_domain()

Split the functionality of msi_create_irq_domain() so it can
be reused for creating per device irq domains.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221124232325.559086358@linutronix.de