MIPS: Tidy EntryLo bit definitions, add PFN

Tidy up the definition of the EntryLo RI & XI bits using BITS_PER_LONG
rather than #ifdef'ing on CONFIG_64BIT, and add a definition for the
offset to the PFN field for use by a later patch.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-kernel@vger.kernel.org
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/11217/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>