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 <[e-mail]>
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/6647/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/include/asm/mips_mt.h

···
 extern unsigned long mt_fpemul_threshold;
 
 extern void mips_mt_regdump(unsigned long previous_mvpcontrol_value);
+
+#ifdef CONFIG_MIPS_MT
 extern void mips_mt_set_cpuoptions(void);
+#else
+static inline void mips_mt_set_cpuoptions(void) { }
+#endif
 
 struct class;
 extern struct class *mt_class;