MIPS: R2: Try to bulletproof instruction_hazard against miss-compilation.

Gcc has a tradition of misscompiling the previous construct using the
address of a label as argument to inline assembler.  Gas otoh has the
annoying difference between la and dla which are only usable for 32-bit
rsp. 64-bit code, so can't be used without conditional compilation.
The alterantive is switching the assembler to 64-bit code which happens
to work right even for 32-bit code ...

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