common: Move serial functions out of common.h

These functions belong in serial.h so move them over.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/board/birdland/bav335x/board.c b/board/birdland/bav335x/board.c
index 8811583a..1f3f44a 100644
--- a/board/birdland/bav335x/board.c
+++ b/board/birdland/bav335x/board.c
@@ -10,6 +10,7 @@
 #include <common.h>
 #include <env.h>
 #include <errno.h>
+#include <serial.h>
 #include <spl.h>
 #include <asm/arch/cpu.h>
 #include <asm/arch/hardware.h>