dri: add a way to request that modes have matching color/zs depths

dri: add a way to request that modes have matching color/zs depths

Some GPUs, notably nv3x/nv4x can't render to mismatched color/zs
framebuffer depths. Fallbacks can be done by the driver, with shadow
surfaces, but no reason to encourage applications to select non-matching
glx visuals.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>