virglrenderer: also allow querying for width/height
With the current API, the VMM always knows the width/height of the resource. The plan is to switch to a size-based API, in which the host library potentially knows these details for 2D, exportable buffers in particular.
To support this potentially in the future, add width/height in export query. We haven't issued a release since this API was added, so this should be good.