drm/xe/engine: add missing rpm for bind engines

Bind engines need to use the migration vm, however we don't have any rpm
for such a vm, otherwise the kernel would prevent rpm suspend-resume.
There are two issues here, first is the actual engine create which needs
to touch the lrc, but since that is in VRAM we trigger loads of missing
mem_access asserts. The second issue is when destroying the actual
engine, which requires GuC CT to deregister the context.

v2 (Rodrigo):
  - Just use ENGINE_FLAG_VM as the indicator that we need to hold an rpm
    ref. This also handles the case in xe_vm_create() where we create
    default bind engines.

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/499
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/504


Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>