env: Move env_get_f() to env.h

Move this function 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/socrates/socrates.c b/board/socrates/socrates.c
index ff465a8..da9ae5b 100644
--- a/board/socrates/socrates.c
+++ b/board/socrates/socrates.c
@@ -11,6 +11,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <pci.h>
 #include <asm/processor.h>
 #include <asm/immap_85xx.h>