RFC: gallium: Add pipe_context::make_resource_shareable
iris will use this to remove compression from textures before sharing
them via eglCreateImage. This is based off intel_miptree_make_shareable from i965.
Alternatively, should pipe_context::flush_resource() be used? The
command description explicitly states that it's useful for sharing:
Flush the resource cache, so that the resource can be used
by an external client. Possible usage:
- flushing a resource before presenting it on the screen
- flushing a resource if some other process or device wants to use itCloses #2678 (closed) (partially?)