gma600: Enable HDMI support

There are still some mysteries left, in particular how (and in
fact if) the EDID is supposed to work on the HDMI port. However
the basic stuff now works and I can plug my Q550 into an HDMI
display and get the expected results.

[v2: cleans up space/tab and other formatting as per Dave's
 request]

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>