[MIPS] R1: Fix hazard barriers to make kernels work on R2 also.

Tested with Malta; inflates malta_defconfig by 3932 bytes.  Ideally there
should be additional configuration to allow getting rid of this overhead
but that would be too much complexity at this stage of the release cycle.

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