[MIPS] time: Move R4000 clockevent device code to separate configurable file

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

include/asm-mips/time.h

@@ -75,6 +75,12 @@ extern int (*perf_irq)(void);
 /*
  * Initialize the calling CPU's compare interrupt as clockevent device
  */
+#ifdef CONFIG_CEVT_R4K
 extern void mips_clockevent_init(void);
+#else
+static inline void mips_clockevent_init(void)
+{
+}
+#endif
 
 #endif /* _ASM_TIME_H */