virgl: modify internal structures to track winsys-supplied data

virgl: modify internal structures to track winsys-supplied data

The winsys might supply dimensions that are different than
those we calculate.  In additional, it may supply virtualized
modifiers.

In practice, a stride != bpp * width and virtualized modifiers don't
happen yet, but the plan is to move in that direction.

Also make virgl_resource_layout static.

Reviewed by: Robert Tarasov <tutankhamen@chromium.org>