By default route the 8254 over the 8259 and only disable
it on ATI boards where this causes double timer interrupts.

This should unbreak some Nvidia boards where the timer doesn't
seem to tick of it isn't enabled in the 8259. At least one
VIA board also seemed to have a little trouble with the disabled
8259.

For 2.6.20 we'll try both dynamically without black listing, but I think
for .19 this is the safer approach because it has been already well tested
in earlier kernels. This also makes the x86-64 behaviour the same
as i386.

Command line options can change all this of course.
Signed-off-by: Andi Kleen <ak@suse.de>