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/nvidia/p2771-0000/p2771-0000.c b/board/nvidia/p2771-0000/p2771-0000.c
index d294c7a..8c91b75f 100644
--- a/board/nvidia/p2771-0000/p2771-0000.c
+++ b/board/nvidia/p2771-0000/p2771-0000.c
@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <environment.h>
 #include <fdtdec.h>
 #include <i2c.h>