env: Add env_export() wrapper

Implement env_export() wrapper, so that all implementers of saveenv() don't
have to call hexport_r(), crc32() etc. sequence . This trims down a bit of
code duplication.

Signed-off-by: Marek Vasut <marex@denx.de>

include/environment.h

@@ -201,6 +201,9 @@ int set_default_vars(int nvars, char * const vars[]);
 /* Import from binary representation into hash table */
 int env_import(const char *buf, int check);
 
+/* Export from hash table into binary representation */
+int env_export(env_t *env_out);
+
 #endif /* DO_DEPS_ONLY */
 
 #endif /* _ENVIRONMENT_H_ */