We piggyback on "x86/acpi: Provide registration for acpi_suspend_lowlevel."
to register a Xen version of the callback. The callback does not
do anything special - except it omits the x86_acpi_suspend_lowlevel.

This is necessary b/c during suspend the generic code tries to write
cr3 values that clashes with what the hypervisor has set up for the guest.
Signed-off-by: NLiang Tang <liang.tang@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: NBen Guthro <benjamin.guthro@citrix.com>
Acked-by: NH. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>