MIPS: Provide empty mips_mt_set_cpuoptions when CONFIG_MIPS_MT=n

MIPS: Provide empty mips_mt_set_cpuoptions when CONFIG_MIPS_MT=n

Both the CONFIG_MIPS_CPS & CONFIG_MIPS_CMP SMP implementations call
mips_mt_set_cpuoptions when preparing to start secondary CPUs. However
both may be used without MT. Provide an empty inline function to prevent
a link error in this case.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6647/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>