Refactor fullmte bits into common dir

Pull fullmte-common and fullmte-vars into a common dir so they can also
be used by other devices. See the topic changes for device/google/gs-common.

Bug: 288843255
Test: run soong for shiba_fullmte, build/flash husky_fullmte.

Change-Id: I6cc636596acff8b5234197fe26f85e27f7e85a62
5 files changed