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

This function belongs in time.h so move it over and add a comment.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

drivers/spi/rk_spi.c

@@ -16,6 +16,7 @@
 #include <dt-structs.h>
 #include <errno.h>
 #include <spi.h>
+#include <time.h>
 #include <linux/errno.h>
 #include <asm/io.h>
 #include <asm/arch-rockchip/clock.h>