vfio/cdx: update driver to build without CONFIG_GENERIC_MSI_IRQ

vfio/cdx: update driver to build without CONFIG_GENERIC_MSI_IRQ

Define dummy MSI related APIs in VFIO CDX driver to build the
driver without enabling CONFIG_GENERIC_MSI_IRQ flag.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202508070308.opy5dIFX-lkp@intel.com/
Reviewed-by: Nikhil Agarwal <nikhil.agarwal@amd.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
Link: https://lore.kernel.org/r/20250826043852.2206008-2-nipun.gupta@amd.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>