virgl: set texture buffer offset alignment to disable ARB_texture_buffer_range.
The host side hasn't got support for this feature yet, so don't enable it
unless we get the caps from the host.
This makes the texture buffer range piglit tests skip now.
Fixes: fe0647df5a7 (virgl: add offset alignment values to to v2 caps struct)
Reviewed-by: Gurchetan Singh <firstname.lastname@example.org>