Starting from GB, modules which doesn't have LOCAL_MODULE_TAGS
defined (default to user tag) or which has user tag and not part
of GRANDFATHERED_USER_MODULES does throgh ERROR/WARNING
message. To supress these WARNING messages, we need to add
optional tag.
Targets tested on:
msm8660_surf
Tests:
Did a build from scratch
Change-Id: I006ae23366cf1f517f0c68f66f607be1455b4ba9