x86/vioapic: expand hvm_vioapic to contain vIO APIC internal state

x86/vioapic: expand hvm_vioapic to contain vIO APIC internal state

This is required in order to have a variable number of vIO APIC pins, instead
of the current fixed value (48). Note that this patch only expands the fields
of the hvm_vioapic struct, without actually introducing any new fields or
functionality.

The reason to expand the hvm_vioapic structure instead of the hvm_hw_vioapic
one is that the variable number of pins functionality is only going to be used
by the hardware domain, so no modifications are needed to the save format.

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