[MIPS] Support /proc/kcore for MIPS

I'm pretty sure that the CKSEG0 bits are wrong, but I did need to
cover that region - because the SB-1 kernel links at 0xffffffff80100000
or so, disassembly and printing static variables don't work unless the
debugger can read that region.

Signed-off-by: Daniel Jacobowitz <dan@codesourcery.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>