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>

drivers/ddr/fsl/fsl_ddr_gen4.c

@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <asm/io.h>
 #include <fsl_ddr_sdram.h>
 #include <asm/processor.h>