intel_iommu: Fix irqchip / X2APIC configuration checks

We don't need to check kvm_enable_x2apic(). It's perfectly OK to support
interrupt remapping even if we can't address CPUs above 254. Kind of
pointless, but still functional.

The check on kvm_enable_x2apic() needs to happen *anyway* in order to
allow CPUs above 254 even without an IOMMU, so allow that to happen
elsewhere.

However, we do require the *split* irqchip in order to rewrite I/OAPIC
destinations. So fix that check while we're here.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Acked-by: Claudio Fontana <cfontana@suse.de>
Message-Id: <20220314142544.150555-4-dwmw2@infradead.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>