qemu: avoid launching non-x86 guests with APIC-EOI setting

qemu: avoid launching non-x86 guests with APIC-EOI setting

The "<apic/>" feature, although it's available only for x86 guests,
can be declared in the domain XML of other archs without errors.
But setting its 'eoi' attribute will break QEMU. For "<apic eoi='on'/>",
in a ppc64 guest:

qemu-kvm: Expected key=value format, found +kvm_pv_eoi

A similar error happens with eoi='off'.

One can argue that it's better to simply forbid launching non-x86
guests with "<apic/>" declared in the XML - it is a feature that
the architecture doesn't support and this would make it clearer
about it. This is sensible, but there are non-x86 guests that are
running with "<apic/>" declared in the domain (and A LOT of guests
running with "<acpi/>" for that matter, probably reminiscent of x86
templates that were reused for other archs) that will stop working if we
go this route.

A more subtle approach is to detect if the 'eoi' element is being set
for non-x86 guests and warn the user about it with a better error
message than the one QEMU provides. This is the new error message
when any value is set for the 'eoi' element in a ppc64 XML:

error: unsupported configuration: The 'eoi' attribute of the 'apic'
feature is not supported for architecture 'ppc64' or machine type
'pseries'.

https://bugzilla.redhat.com/show_bug.cgi?id=1236440

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>