virgl: don't a use staging when a resources created with the shared flag

virgl: don't a use staging when a resources created with the shared flag

There seems to be a problem with running firefox by using Xwayland that
results in a shared resources being not always tagged as using staging.

As a result one process tries to map the resource that was allocated as
one that uses staging without actually using the staging resource, and
hence the mapped range only accounts for the small region that we have
to allocated because a zero-allocation doesn't work, but the application
mapping the resource assumes that a properly sized range is mapped, and
consequently this results in invalid memory access.

To work around this issue disable creating staging for resources that
are created by using shared binding. It is not clear to me whether this
is the best fix, but it seems to quell the issue.

Fixes: c9d99b7eec7ec14d6d71d381a424b6280d75a882
    virgl: Fix texture transfers by using a staging resource

Related: https://gitlab.freedesktop.org/virgl/virglrenderer/-/issues/291
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19655>