MADT Multiprocessor Wakeup structure version 1 brings support for CPU offlining:
BIOS provides a reset vector where the CPU has to jump to for offlining itself.
The new TEST mailbox command can be used to test whether the CPU offlined itself
which means the BIOS has control over the CPU and can online it again via the
ACPI MADT wakeup method.

Add CPU offlining support for the ACPI MADT wakeup method by implementing custom
cpu_die(), play_dead() and stop_this_cpu() SMP operations.

CPU offlining makes it possible to hand over secondary CPUs over kexec, not
limiting the second kernel to a single CPU.

The change conforms to the approved ACPI spec change proposal. See the Link.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Kai Huang <kai.huang@intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Tao Liu <ltao@redhat.com>
Link: https://lore.kernel.org/all/13356251.uLZWGnKmhe@kreacher
Link: https://lore.kernel.org/r/20240614095904.1345461-19-kirill.shutemov@linux.intel.com