MIPS: Probe for small (1KiB) page support

Probe Config3 for small page support. This will be useful to give clues
as to whether the PageGrain register exists.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10722/


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