mesa/st: Test round-tripping of all compressed formats.

mesa/st: Test round-tripping of all compressed formats.

We checked round-tripping of formats without fallbacks, but weren't
setting the compression support flags in the mock context and thus
needed to skip testing those.  Just set all the flags and assert that
no fallbacks are triggered, so we get full test coverage.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>