[VOYAGER] fix genirq mess

The implementation of genirq in x86 completely broke voyager (and
presumably visws).  Since it's plugged into so much of the x86
infrastructure, you can't expect it to work unconverted.

This patch introduces a voyager IRQ handler type and switches voyager
to the genirq infrastructure.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>