egl/gbm: Fix juicy refactor fallout
So far:
- Fix surfaceless+android modifiers
- Add option to un-version libgallium_dri for Android and CrOS to use
So far, this at least gets CrOS UI working. Android (arcvm) is still unhappy, which I'm still trying to track down. (Unhelpfully android immediately reboots when SF fails to come up.)