env: Move env_get_hex() to env.h

Move env_get_hex() over to the new header file.

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

cmd/elf.c

@@ -16,6 +16,7 @@
 #include <common.h>
 #include <command.h>
 #include <elf.h>
+#include <env.h>
 #include <environment.h>
 #include <net.h>
 #include <vxworks.h>