xf86-video-ati: Changes to 'evergreen_accel'

[Alex Deucher]

New branch 'evergreen_accel' available with the following commits:
commit 6930d2c981221757b1e11ef194809f085753a611
Author: Alex Deucher <alexdeucher at gmail.com>
Date:   Fri Aug 20 16:55:21 2010 -0400

    Add initial EXA and Xv support for evergreen
    
    Based on the r6xx/r7xx code updated for evergreen.
    Still causes GPU hangs in some cases.  We haven't
    tracked down why yet.  Might be related to constant
    buffer persistence.
    
    Signed-off-by: Alex Deucher <alexdeucher at gmail.com>