drm/xe: Take a ref to xe file when user creates a VM

Take a reference to xef when user creates the VM and put the reference
when user destroys the VM.

Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240718210548.3580382-4-umesh.nerlige.ramappa@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>