Supported Android versions

fbf5c0ca introduces build-time warning for GRALLOC_HANDLE_VERSION < 4 (Ref. platformdrmgeneric.cpp), but composer is built with -Werror (ref. Android.bp).

This brakes compatibility with older Android versions (Android-10 and earlier) unless libdrm will be upgraded to v2.4.97 which might be undesirable for some projects.

If previous Android versions are deprecated at some point, it would be useful to mark the latest composer revision compatible with them (e.g. introduce a tag or a branch).

Also it would be useful if information regarding supported Android versions will be mentioned somewhere (e.g. included in README).