Restrict AVD and VD parsing to the current element instead of the whole document

This CL changes the AVD xml parsing to parsing only within the current
element, which prevents AVD parsing from always skipping to the end of
the doucment. So things that are defined after AVD in the same document
can be picked up by the xml parser.

The same fix has been applied to VD as well.

BUG: 31865175
Test: Manually following comment #1 in the bug above

Change-Id: I4ebdce1eb2e92d6f6e2c37caed9607253d24602f