svga: Add a more elaborate format compatibility determination v2

svga: Add a more elaborate format compatibility determination v2

dri3 is a bit sloppy about its format compatibility requirements, so add
a possibility to import xrgb surfaces as argb textures and vice versa.

At the same time, make the svga_texture_from_handle() function a bit more
readable and fix the error path where we leaked a winsys surface.

v2: Addressed review comments by Brian.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Charmaine Lee <charmainel@vmware.com>