svga: mark dest image as defined in svga_surface_copy()

svga: mark dest image as defined in svga_surface_copy()

After we blit/copy to a dest texture image we need to mark it as
being defined.  This fixes broken mipmap generation for quite a
few texture formats.  Mipgen involves making texture views and
svga_texture_view_surface() skips texture images that are undefined.

Cc: "10.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: José Fonseca <jfonseca@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>