x86/xen: disable CPU idle and frequency drivers for PVH dom0

When running as a PVH dom0 the ACPI tables exposed to Linux are (mostly)
the native ones, thus exposing the C and P states, that can lead to
attachment of CPU idle and frequency drivers.  However the entity in
control of the CPU C and P states is Xen, as dom0 doesn't have a full view
of the system load, neither has all CPUs assigned and identity pinned.

Like it's done for classic PV guests, prevent Linux from using idle or
frequency state drivers when running as a PVH dom0.

On an AMD EPYC 7543P system without this fix a Linux PVH dom0 will keep the
host CPUs spinning at 100% even when dom0 is completely idle, as it's
attempting to use the acpi_idle driver.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Message-ID: <20250407101842.67228-1-roger.pau@citrix.com>