Resources created with modifiers are treated as scanout because there is
no way for applications to specify the usage (though that capability may
be useful to have in the future). Currently all the resources created by
applications with modifiers are for scanout, so make sure they have bind
flags set accordingly.

This is necessary in order to properly export buffers for such resources
so that they can be shared with scanout hardware.

Tested-by: Daniel Kolesa <daniel@octaforge.org>
Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Thierry Reding <treding@nvidia.com>