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>

common/autoboot.c

@@ -9,6 +9,7 @@
 #include <bootretry.h>
 #include <cli.h>
 #include <console.h>
+#include <env.h>
 #include <fdtdec.h>
 #include <hash.h>
 #include <memalign.h>