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/common/spl/spl_net.c b/common/spl/spl_net.c
index c91ad2b..8033032 100644
--- a/common/spl/spl_net.c
+++ b/common/spl/spl_net.c
@@ -7,6 +7,7 @@
  * Ilya Yanok <ilya.yanok@gmail.com>
  */
 #include <common.h>
+#include <env.h>
 #include <errno.h>
 #include <spl.h>
 #include <net.h>