drm: add X600 PCI IDs

From: Brice Goglin <Brice.Goglin@ens-lyon.org>

Now that Xorg 6.9/7.0 has been released, DRI is supported on more Radeon
cards without ATI proprietary drivers.  I got my X300 to work without
problem.  But, another Radeon X600 required to add its PCI ids to the
Radeon driver.  Patch is attached.

I can't be sure about the "CHIP_RV350", I copied it from the X300 entry
(from http://dri.freedesktop.org/wiki/ATIRadeon

, X600 is a rv380 chip while
X300 is a rv370).  But, at least it works now.

Signed-off-by: Brice Goglin <Brice.Goglin@ens-lyon.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Dave Airlie <airlied@linux.ie>