PCI: vmd: Offset Client VMD MSI-X vectors

Client VMD platforms have a software-triggered MSI-X vector 0 that will
not forward hardware-remapped MSI from the sub-device domain. This
causes an issue with VMD platforms that use AHCI behind VMD and have a
single MSI-X vector remapped to VMD vector 0. Add a VMD MSI-X vector
offset for these platforms.

Link: https://lore.kernel.org/r/20201102222223.92978-1-jonathan.derrick@intel.com


Tested-by: Jian-Hong Pan <jhp@endlessos.org>
Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>