minigbm: add option to force 256 byte alignment of linear buffers

minigbm: add option to force 256 byte alignment of linear buffers

BUG=b:172617736
TEST=run glxgears crostini on mushu

Change-Id: I0a5934e3676a70dd0bdb5f53701114fb0c19f016
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/minigbm/+/2522635
Reviewed-by: David Riley <davidriley@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Dominik Behr <dbehr@chromium.org>
Auto-Submit: Dominik Behr <dbehr@chromium.org>
Commit-Queue: Dominik Behr <dbehr@chromium.org>