drm/xe: don't allocate under ct->lock

Seems to be a sensitive lock, where ct->lock looks to be primed with
fs_reclaim, so holding that and then allocating memory will cause
lockdep to complain. We need to change the ordering wrt to grabbing the
ct->lock and potentially grabbing the runtime_pm, since some of the
runtime_pm routines can allocate memory (or at least that's what lockdep
seems to suggest).

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>