MIPS: BMIPS: Add set/clear CP0 macros for BMIPS operations

Several BMIPS-specific CP0 registers are used for SMP boot and other
operations.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2956/


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