env: Move env_get() to env.h

Move env_get() over to the new header file.

Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/freescale/bsc9131rdb/bsc9131rdb.c b/board/freescale/bsc9131rdb/bsc9131rdb.c
index 9d9c83f..30e7a1f 100644
--- a/board/freescale/bsc9131rdb/bsc9131rdb.c
+++ b/board/freescale/bsc9131rdb/bsc9131rdb.c
@@ -9,6 +9,7 @@
 #include <asm/cache.h>
 #include <asm/immap_85xx.h>
 #include <asm/io.h>
+#include <env.h>
 #include <miiphy.h>
 #include <linux/libfdt.h>
 #include <fdt_support.h>