common: Move timer_get_us() function out of common.h

This function belongs in time.h so move it over and update the comment
style.
Signed-off-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NTom Rini <trini@konsulko.com>

include/common.h

@@ -251,9 +251,6 @@ void	irq_install_handler(int, interrupt_handler_t *, void *);
 void	irq_free_handler   (int);
 void	reset_timer	   (void);
 
-/* Return value of monotonic microsecond timer */
-unsigned long timer_get_us(void);
-
 void	enable_interrupts  (void);
 int	disable_interrupts (void);
 

include/time.h

@@ -96,4 +96,11 @@ ulong ticks2usec(unsigned long ticks);
  */
 void wait_ticks(unsigned long ticks);
 
+/**
+ * timer_get_us() - Get monotonic microsecond timer
+ *
+ * @return value of monotonic microsecond timer
+ */
+unsigned long timer_get_us(void);
+
 #endif /* _TIME_H */