Revert "drm/radeon: do not move bo to different placement at each cs"

This reverts commit d025e9e2

.

This causes corruption for a number of users and needs further
investigation in the next cycle.
https://bugzilla.kernel.org/show_bug.cgi?id=52491
https://bugs.freedesktop.org/show_bug.cgi?id=58659
http://lists.freedesktop.org/archives/dri-devel/2013-January/032961.html

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>