genirq/irqdomain: Move bus token enum into a seperate header

Split the bus token defines out into a seperate header file to avoid
inclusion of irqdomain.h in msi.h.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20221111122014.237221143@linutronix.de