xen/arm: traps: MMIO should only be emulated for fault translation

xen/arm: traps: MMIO should only be emulated for fault translation

The function do_trap_data_abort_guest assumes that a stage-2 data abort
can only be taken for a translation fault or permission fault today.

Whilst this is true today, it might not be in the future. Rather than
emulating the MMIO for any fault other than the permission one, print
a warning message when the fault is not handled by Xen.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>