i386/xen: handle upcall related hypercalls

i386/xen: handle upcall related hypercalls

It handles HVMOP_set_param(.index = HVM_PARAM_CALLBACK_IRQ) which
sets the upcall IRQ from the guest. This is not a APIC asserted
vector and hence we need to add a new special irqchip route which
further requires special hypervisor enlightment. We gate enabling
this with KVM_CAP_XEN_HVM_GUEST which has the necessary irqchip
route type support.

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>