KVM: PPC: Book3S HV: Use XICS hypercalls when running as a nested hypervisor

KVM: PPC: Book3S HV: Use XICS hypercalls when running as a nested hypervisor

This adds code to call the H_IPI and H_EOI hypercalls when we are
running as a nested hypervisor (i.e. without the CPU_FTR_HVMODE cpu
feature) and we would otherwise access the XICS interrupt controller
directly or via an OPAL call.

Reviewed-by: David Gibson <[email protected]>
Signed-off-by: Paul Mackerras <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>