Add a handful of simple functions for accessing QEMU's hotplug registers more conveniently. These functions thinly wrap some of the registers described in "docs/specs/acpi_cpu_hotplug.txt" in the QEMU tree. The functions hang (by design) if they encounter an internal failure. Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Igor Mammedov <imammedo@redhat.com> Cc: Jiewen Yao <jiewen.yao@intel.com> Cc: Jordan Justen <jordan.l.justen@intel.com> Cc: Michael Kinney <michael.d.kinney@intel.com> Cc: Philippe Mathieu-Daudé <philmd@redhat.com> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1512 Signed-off-by: Laszlo Ersek <lersek@redhat.com> Message-Id: <20200226221156.29589-8-lersek@redhat.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com> Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>