Add ref counting for xe_file.

v2:
- Add kernel doc for exported functions (Matt)
- Instead of xe_file_destroy, export the get/put helpers (Lucas)

v3: Fixup the kernel-doc format and description (Matt, Lucas)
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240718210548.3580382-3-umesh.nerlige.ramappa@intel.comSigned-off-by: Lucas De Marchi <lucas.demarchi@intel.com>