env: Move get_env_id() to env.h

Move this function over to the new header file. Also rename it to have an
env_ prefix like the other functions.

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

include/env.h

@@ -11,6 +11,16 @@
 
 #include <stdbool.h>
 
+/**
+ * env_get_id() - Gets a sequence number for the environment
+ *
+ * This value increments every time the environment changes, so can be used an
+ * an indication of this
+ *
+ * @return environment ID
+ */
+int env_get_id(void);
+
 /**
  * env_complete() - return an auto-complete for environment variables
  *