matroxfb: rectify jitter (G450/G550)

This builds upon my previous attempts to resolve some jitter problems seen
with the Matrox G450 and G550 -based cards, including odd disparities observed
between x86 and Power -based machines in a somewhat less hackish way (removing
the hacked ifdefs).

Apparently, preference should be given to use the DVI PLL when frequencies
permit, the Standard PLL otherwise.  The max pixel clock for the panellink
interface is extracted from the PInS information on the card and used as a
limit to determine which PLL to use.

Signed-off-by: Paul A. Clarke <pc@us.ibm.com>
Acked-by: Petr Vandrovec <petr@vandrovec.name>
Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>