radeon: incorrect crtc for external LCD on VGA-0

[Otto Solares]

Hi!

Video card on x86 laptop:

ATI Technologies Inc Radeon R250 [Mobility FireGL 9000] (rev 02)

I used to have an old external CRT monitor attached to the VGA-0
connector and the command `xrand --output LVDS --off` would
correctly turn off the laptop's LCD so I can work in the external
without having both monitors powered-on.

Problem now is that I buy a new external LCD monitor and the
above command would turn off both the new LCD and the laptop's
LCD.

But when `xrandr --output VGA-0 --crtc 0` everything works as
expected so I pressume is a bug in the crtc detection when a
LCD is attached in the VGA-0 connector both monitors are driven
by the same crtc.  As I said, plugging the CRT monitor doesn't
exhibit this problem.

Running latest Debian Sid (X Server 1.4.0) and git radeon driver.

-otto