xen/ACPI: don't upload Px/Cx data for disabled processors

This is unnecessary and triggers a warning in the hypervisor.

Often systems have more processor entries in their ACPI tables than are
actually installed/active. The ACPI_STA_DEVICE_PRESENT bit cannot be
reliably used, but the ACPI_MADT_ENABLED bit can. In order to not
introduce new functions in the main ACPI processor driver code, simply
use acpi_get_phys_id(), which does more than we need, but which checks
the MADT enabled bit in the process. Any CPU for which we can't
determine the APIC ID is unlikely to work properly anyway, so the extra
checks done by acpi_get_phys_id() should do no harm.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>