x86: remove VISWS and PARAVIRT around NR_IRQS puzzle

Impact: fix warning message when PARAVIRT is set in config

Remove stale #ifdef components from our IRQ sizing logic.
x86/Voyager is the only holdout.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>