x86/hvm: don't force vCPU 0 for IRQ 0 when using fixed destination mode

x86/hvm: don't force vCPU 0 for IRQ 0 when using fixed destination mode

When the IO APIC pin mapped to the ISA IRQ 0 has been configured to
use fixed delivery mode, do not forcefully route interrupts to vCPU 0,
as the OS might have setup those interrupts to be injected to a
different vCPU, and injecting to vCPU 0 can cause the OS to miss such
interrupts or errors to happen due to unexpected vectors being
injected on vCPU 0.

In order to fix remove such handling altogether for fixed destination
mode pins and just inject them according to the data setup in the
IO-APIC entry.

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