vfio/pci: Probe and store ability to support dynamic MSI-X

Not all MSI-X devices support dynamic MSI-X allocation. Whether
a device supports dynamic MSI-X should be queried using
pci_msix_can_alloc_dyn().

Instead of scattering code with pci_msix_can_alloc_dyn(),
probe this ability once and store it as a property of the
virtual device.

Suggested-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/f1ae022c060ecb7e527f4f53c8ccafe80768da47.1683740667.git.reinette.chatre@intel.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>