drm/xe/pf: fix VFIO link error

drm/xe/pf: fix VFIO link error

The Makefile logic for building xe_sriov_vfio.o was added incorrectly,
as setting CONFIG_XE_VFIO_PCI=m means it doesn't get included into a
built-in xe driver:

ERROR: modpost: "xe_sriov_vfio_stop_copy_enter" [drivers/vfio/pci/xe/xe-vfio-pci.ko] undefined!
ERROR: modpost: "xe_sriov_vfio_stop_copy_exit" [drivers/vfio/pci/xe/xe-vfio-pci.ko] undefined!
ERROR: modpost: "xe_sriov_vfio_suspend_device" [drivers/vfio/pci/xe/xe-vfio-pci.ko] undefined!
ERROR: modpost: "xe_sriov_vfio_wait_flr_done" [drivers/vfio/pci/xe/xe-vfio-pci.ko] undefined!
ERROR: modpost: "xe_sriov_vfio_error" [drivers/vfio/pci/xe/xe-vfio-pci.ko] undefined!
ERROR: modpost: "xe_sriov_vfio_resume_data_enter" [drivers/vfio/pci/xe/xe-vfio-pci.ko] undefined!
ERROR: modpost: "xe_sriov_vfio_resume_device" [drivers/vfio/pci/xe/xe-vfio-pci.ko] undefined!
ERROR: modpost: "xe_sriov_vfio_resume_data_exit" [drivers/vfio/pci/xe/xe-vfio-pci.ko] undefined!
ERROR: modpost: "xe_sriov_vfio_data_write" [drivers/vfio/pci/xe/xe-vfio-pci.ko] undefined!
ERROR: modpost: "xe_sriov_vfio_migration_supported" [drivers/vfio/pci/xe/xe-vfio-pci.ko] undefined!
WARNING: modpost: suppressed 3 unresolved symbol warnings because there were too many)

Check for CONFIG_XE_VFIO_PCI being enabled in the Makefile to decide whether to
include the object instead.

Fixes: 17f22465c5a5 ("drm/xe/pf: Export helpers for VFIO")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patch.msgid.link/20251204094154.1029357-1-arnd@kernel.org