drm/xe: Add build on bug to assert page fault queue works

drm/xe: Add build on bug to assert page fault queue works

If PF_QUEUE_NUM_DW % PF_MSG_LEN_DW != 0 then the page fault queue logic
does not work when wrapping occurs. Add a build bug on to assert
PF_QUEUE_NUM_DW % PF_MSG_LEN_DW == 0 to enforce this restriction and
document the code.

v2:
- s/NUM_PF_QUEUE/PF_QUEUE_NUM_DW (Brian)

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>