drm/xe: Relax runtime pm protection around VM

drm/xe: Relax runtime pm protection around VM

In the regular use case scenario, user space will create a
VM, and keep it alive for the entire duration of its workload.

For the regular desktop cases, it means that the VM
is alive even on idle scenarios where display goes off. This
is unacceptable since this would entirely block runtime PM
indefinitely, blocking deeper Package-C state. This would be
a waste drainage of power.

Limit the VM protection solely for long-running workloads that
are not protected by the scheduler references.
By design, run_job for long-running workloads returns NULL and
the scheduler drops all the references of it, hence protecting
the VM for this case is necessary.

v2: Update commit message to a more imperative language and to
    reflect why the VM protection is really needed.
    Also add a comment in the code to let the reason visbible.

v3: Remove vma_access case and the mentions to mmap. Mmap cases
    are already protected by the gem page fault.

Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Tested-by: Francois Dugast <francois.dugast@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240522170105.327472-4-rodrigo.vivi@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>