st/va: Implement vaExportSurfaceHandle()

st/va: Implement vaExportSurfaceHandle()

This is a new interface in libva2 to support wider use-cases of passing
surfaces to external APIs.  In particular, this allows export of NV12 and
P010 surfaces.

v2: Convert surfaces to progressive before exporting them (Christian).

v3: Set destination rectangle to match source when converting (Leo).
    Add guards to allow building with libva1.

Signed-off-by: Mark Thompson <sw@jkqxz.net>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-and-Tested-by: Leo Liu <leo.liu@amd.com>