powerpc/xmon: Check for HV mode when dumping XIVE info from OPAL

powerpc/xmon: Check for HV mode when dumping XIVE info from OPAL

Currently, the xmon 'dx' command calls OPAL to dump the XIVE state in
the OPAL logs and also outputs some of the fields of the internal XIVE
structures in Linux. The OPAL calls can only be done on baremetal
(PowerNV) and they crash a pseries machine. Fix by checking the
hypervisor feature of the CPU.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190814154754.23682-2-clg@kaod.org