Add a new parameter to DOMCTL_bind_pt_irq to allow Xen to know the
guest physical address of MSI-X table. Also add a new MMIO intercept
handler to intercept that gpa in order to handle MSI-X vector mask
bit operation in the hypervisor. This reduces the load of device model
considerably if the guest does mask and unmask frequently
Signed-off-by: Qing He <qing.he@intel.com>