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>
diff --git a/drivers/net/pic32_eth.c b/drivers/net/pic32_eth.c
index 5c706c0..b0f7677 100644
--- a/drivers/net/pic32_eth.c
+++ b/drivers/net/pic32_eth.c
@@ -9,6 +9,7 @@
 #include <net.h>
 #include <miiphy.h>
 #include <console.h>
+#include <time.h>
 #include <wait_bit.h>
 #include <asm/gpio.h>