drm/xe/selftests: hold rpm for evict_test_run_device()

We are calling fairly low level things like xe_bo_restore_kernel() which
expect caller to be holding mem_access.ref. Since we are doing stuff
like evict_all we likely don't want to race with rpm suspend, since that
potentially wants to do the same thing, so just wrap the whole test.

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