i386/xen: implement HVMOP_set_param This is the hook for adding the HVM_PARAM_CALLBACK_IRQ parameter in a subsequent commit. Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com> Signed-off-by: Joao Martins <joao.m.martins@oracle.com> [dwmw2: Split out from another commit] Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> Reviewed-by: Paul Durrant <paul@xen.org>