env: Move env_init() to env.h

Move env_init() over to the new header file.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/board/ti/am335x/board.c b/board/ti/am335x/board.c
index 2c32b92..58d09f7 100644
--- a/board/ti/am335x/board.c
+++ b/board/ti/am335x/board.c
@@ -9,6 +9,7 @@
 
 #include <common.h>
 #include <dm.h>
+#include <env.h>
 #include <errno.h>
 #include <spl.h>
 #include <serial.h>