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/env/env.c b/env/env.c
index d3cbe2f..9d421e8 100644
--- a/env/env.c
+++ b/env/env.c
@@ -5,6 +5,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <environment.h>
 
 DECLARE_GLOBAL_DATA_PTR;