virgl: Add debug flag to bypass driconf to enable the BGRA tweaks

This useful for testing, also because with vtest the dri configuration
is not read.

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
10 jobs for !626 with virgl-add-tweak-if-emulate-bgra-v2 in 9 minutes and 54 seconds (queued for 1 second)
merge request