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>

src/mesa/state_tracker/tests/st_format.c

@@ -56,6 +56,9 @@ int main(int argc, char **argv)
    };
    struct st_context local_st = {
       .pipe = &pctx,
+      .has_etc1 = true,
+      .has_etc2 = true,
+      .has_astc_2d_ldr = true,
    };
    struct st_context *st = &local_st;
 
@@ -65,8 +68,7 @@ int main(int argc, char **argv)
    for (i = 1; i < MESA_FORMAT_COUNT; i++) {
       enum pipe_format pf;
 
-      if (st_compressed_format_fallback(st, i))
-         continue;
+      assert(!st_compressed_format_fallback(st, i));
 
       pf = st_mesa_format_to_pipe_format(st, i);
       if (pf != PIPE_FORMAT_NONE) {