Michel Dänzer authored Mar 18, 2015 and Michel Dänzer committed Jun 15, 2015

When this option is enabled, most pixmaps (including the screen pixmap)
are allocated in system RAM and mostly accessed by the CPU. Changed areas
of the screen pixmap are copied to dedicated per-CRTC scanout pixmaps
regularly, triggered by the vblank interrupt.

(Cherry picked from radeon commits ae92d1765fa370a8d94c2856ad6c45d273ec3c69
and 1af044d7eee211fd4b248c236280274a68334da5)

[ Michel Dänzer: Additional adjustements for the amdgpu driver ]

Signed-off-by: Darren Powell <darren.powell@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>