MIPS: Redefine value of BRK_BUG.

MIPS: Redefine value of BRK_BUG.

The BRK_BUG value is used in the BUG and __BUG_ON inline macros. For
standard MIPS cores the code in the 'tne' instruction is 10-bits long.
In microMIPS, the 'tne' instruction is recoded and the code can only be
4-bits long. We change the value to 12 instead of 512 so that both classic
and microMIPS kernels build.

[ralf@linux-mips.org: Many of the break codes starting from 0 are used
across many MIPS UNIX variants.  Codes starting from 512 are operating
system specific additions.  1023 again is also used by other operating
systems]

Signed-off-by: Steven J. Hill <sjhill@mips.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>