drm: Add general-purpose packet for manipulating scratch registers (r300)

From: Aapo Tahkola (via DRM CVS)
Signed-off-by: Dave Airlie <airlied@linux.ie>

diff --cc drivers/char/drm/r300_cmdbuf.c
Simple merge

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

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