[PATCH] matroxfb: fix jittery display on non-ppc systems

I wish I was happier about this patch.  It'll serve as a placeholder for
the moment.  I'm still trying to get a G550 working in order to even
reproduce the problem this patch introduces.  I find that the G450 has
jitter even without this patch, so it won't show me what the patch changed.
 At this point, I'll continue trying to get the G550 to work, and in
parallel work with the G450 to work out the kinks.

The patch is below.

Set XDVICLKCTRL only on PPC, as doing this apparently introduces jitter on
the G550, at least on x86 architectures.

Signed-off-by: Paul A. Clarke <pc@us.ibm.com>
Signed-off-by: Petr Vandrovec <petr@vandrovec.name>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>