x86/dom0: propagate PVH vlapic EOIs to hardware

x86/dom0: propagate PVH vlapic EOIs to hardware

Current check for MSI EIO is missing a special case for PVH Dom0,
which doesn't have a hvm_irq_dpci struct but requires EIOs to be
forwarded to the physical lapic for passed-through devices.

Add a short-circuit to allow EOIs from PVH Dom0 to be propagated.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Juergen Gross <jgross@suse.com>