On many of the newer MIPS32 cores, CP0 CONFIG2 bit 12 (L2B) indicates
that the L2 cache is disabled and therefore Linux should not attempt
to use it.

[Ralf: Moved the code added by Kevin's original patch into a separate
function that can easily be replaced for platforms that need more a
different probe.]
Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Cc: linux-mips@linux-mips.org>
Cc: <linux-kernel@vger.kernel.org>
Patchwork: https://patchwork.linux-mips.org/patch/1723/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>