package/mesa3d: Refactor XA support to prepare support for ATI drivers

[Thomas:
  - move the new blind option next to the other existing blind options
    in the package.
  - edit the commit log to remove the changelog.]

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>