x86/PVH: avoid call to handle_mmio

x86/PVH: avoid call to handle_mmio

handle_mmio() is currently unsafe for pvh guests. A call to it would
result in call to vioapic_range that will crash xen since the vioapic
ptr in struct hvm_domain is not initialized for pvh guests.

However, one path exists for such a call. If a pvh guest, dom0 or domU,
unintentionally touches non-existing memory, an EPT violation would occur.
This would result in unconditional call to hvm_hap_nested_page_fault. In
that function, because get_gfn_type_access returns p2m_mmio_dm for non
existing mfns by default, handle_mmio() will get called. This would result
in xen crash instead of the guest crash. This patch addresses that.

Signed-off-by: Mukesh Rathor <mukesh.rathor@oracle.com>