arm64: kdump: implement machine_crash_shutdown()

arm64: kdump: implement machine_crash_shutdown()

Primary kernel calls machine_crash_shutdown() to shut down non-boot cpus
and save registers' status in per-cpu ELF notes before starting crash
dump kernel. See kernel_kexec().
Even if not all secondary cpus have shut down, we do kdump anyway.

As we don't have to make non-boot(crashed) cpus offline (to preserve
correct status of cpus at crash dump) before shutting down, this patch
also adds a variant of smp_send_stop().

Signed-off-by: AKASHI Takahiro <[email protected]>
Reviewed-by: James Morse <[email protected]>
Acked-by: Catalin Marinas <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>