drm/radeon: fix pixcache and purge/cache flushing registers

Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --cc drivers/char/drm/r300_reg.h
Simple merge

diff --cc drivers/char/drm/radeon_cp.c
Simple merge

diff --cc drivers/char/drm/radeon_drv.h
Simple merge