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/cmd/fpga.c b/cmd/fpga.c
index 9fc2df6..b1c7b54 100644
--- a/cmd/fpga.c
+++ b/cmd/fpga.c
@@ -9,6 +9,7 @@
  */
 #include <common.h>
 #include <command.h>
+#include <env.h>
 #include <fpga.h>
 #include <fs.h>
 #include <gzip.h>