drm/xe: standardize vm-less kernel submissions

drm/xe: standardize vm-less kernel submissions

The current only submission in the driver that doesn't use a vm is the
WA setup. We still pass a vm structure (the migration one), but we don't
actually use it at submission time and we instead have an hack to use
GGTT for this particular engine.
Instead of special-casing the WA engine, we can skip providing a VM and
use that as selector for whether to use GGTT or PPGTT. As part of this
change, we can drop the special engine flag for the WA engine and switch
the WA submission to use the standard job functions instead of dedicated
ones.

v2: rebased on s/engine/exec_queue

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20230822173334.1664332-4-daniele.ceraolospurio@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>