These flags got added as necessary and have no obvious structure. For
feature support checks and masking it's convenient to have two blocks of
flags:

   1) Flags to control the internal behaviour like allocating/freeing
      MSI descriptors. Those flags do not need any support from the
      underlying MSI parent domain. They are mostly under the control
      of the outermost domain which implements the actual MSI support.

   2) Flags to expose features, e.g. PCI multi-MSI or requirements
      which can depend on a underlying domain.

No functional change.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NJason Gunthorpe <jgg@nvidia.com>
Reviewed-by: NKevin Tian <kevin.tian@intel.com>
Acked-by: NMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221124232325.322714918@linutronix.de