MIPS: Apply `.insn' to fixup labels throughout

Fix the issue with the ISA bit being lost in fixups that jump to labels
placed just before a section switch.  Such a switch leads to the ISA bit
being lost, because GAS concludes there is no code that follows and
therefore the label refers to data.  Use the `.insn' pseudo-op to
convince the tool this is not the case.

This lack of label annotation leads to microMIPS compilation errors
like:

mips-linux-gnu-ld: arch/mips/built-in.o: .fixup+0x3b8: Unsupported jump between ISA modes; consider recompiling with interlinking enabled.
mips-linux-gnu-ld: final link failed: Bad value

Signed-off-by: Maciej W. Rozycki <macro@codesourcery.com>
Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8483/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>