acpi: cpuhp: add CPHP_GET_CPU_ID_CMD command

acpi: cpuhp: add CPHP_GET_CPU_ID_CMD command

Firmware can enumerate present at boot APs by broadcasting wakeup IPI,
so that woken up secondary CPUs could register them-selves.
However in CPU hotplug case, it would need to know architecture
specific CPU IDs for possible and hotplugged CPUs so it could
prepare environment for and wake hotplugged AP.

Reuse and extend existing CPU hotplug interface to return architecture
specific ID for currently selected CPU in 2 registers:
 - lower 32 bits in ACPI_CPU_CMD_DATA_OFFSET_RW
 - upper 32 bits in ACPI_CPU_CMD_DATA2_OFFSET_R

On x86, firmware will use CPHP_GET_CPU_ID_CMD for fetching the APIC ID
when handling hotplug SMI.

Later, CPHP_GET_CPU_ID_CMD will be used on ARM to retrieve MPIDR,
which serves the similar to APIC ID purpose.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <1575896942-331151-10-git-send-email-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>