Add field definitions for some of the 64-bit specific Hardware page
Table Walker (HTW) register fields in PWSize and PWCtl, in preparation
for fixing the 64-bit HTW configuration.

Also print these fields out along with the others in print_htw_config().
Signed-off-by: NJames Hogan <james.hogan@imgtec.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13363/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>