MIPS: microMIPS: Disable LL/SC and fix linker bug.

Partially revert commit e0c14a260d66ba35935600d6435940a566fe806b
and turn off LL/SC when building a pure microMIPS kernel. This is
a temporary fix until the cmpxchg assembly macro functions are
re-written to not use the HI/LO registers in address calculations.

Also add .insn in selected user access functions which would
otherwise produce ISA mode jump incompatibilities. This is also a
temporary fix.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>