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/arch/powerpc/cpu/mpc85xx/fdt.c b/arch/powerpc/cpu/mpc85xx/fdt.c
index 20ecca6..d17c382 100644
--- a/arch/powerpc/cpu/mpc85xx/fdt.c
+++ b/arch/powerpc/cpu/mpc85xx/fdt.c
@@ -7,6 +7,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <environment.h>
 #include <linux/libfdt.h>
 #include <fdt_support.h>