rtl8721csm/download: Support erasing secure storage in dbuild
Add option to support erasing secure storage in dbuild.
<option desc="Flash TizenRT ota">OTA</option>
<option desc="Erase TizenRT kernel">ERASE KERNEL</option>
<option desc="Erase TizenRT ota">ERASE OTA</option>
+ <option desc="Erase TizenRT Secure Storage">ERASE SS</option>
<option desc="Erase TizenRT userfs">ERASE USERFS</option>
<option desc="Erase all binaries and images">ERASE ALL</option>
</options>
