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/ti/dra7xx/evm.c b/board/ti/dra7xx/evm.c
index 74d04bb..ea85235 100644
--- a/board/ti/dra7xx/evm.c
+++ b/board/ti/dra7xx/evm.c
@@ -13,6 +13,7 @@
 #include <env.h>
 #include <palmas.h>
 #include <sata.h>
+#include <serial.h>
 #include <linux/string.h>
 #include <asm/gpio.h>
 #include <usb.h>