env: Move env_set_hex() to env.h

Move env_set_hex() over to the new header file along with env_set_addr()
which uses it.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

cmd/cbfs.c

@@ -8,6 +8,7 @@
  */
 #include <common.h>
 #include <command.h>
+#include <env.h>
 #include <cbfs.h>
 
 static int do_cbfs_init(cmd_tbl_t *cmdtp, int flag, int argc,