avmediaogl: build depends on ENABLE_GLTF instead

Change-Id: I03d0d7c0446b6316e388ae717aded6bb7dcc88f1
configure.ac: remove duplicated flag

Change-Id: I95ee315fe1c10ae95ea0fe940eca4c06a6326447
Introduce a new building flag to enable/disable gltf support

Enable it by defautl excepting android and ios.

Change-Id: I7798661ad7e470ad1eb91060ec21ba1de3979a4b