arm/acpi: Add ACPI support for SMP initialization

arm/acpi: Add ACPI support for SMP initialization

ACPI 5.1 only has two explicit methods to boot up SMP, PSCI and Parking
protocol, but the Parking protocol is only specified for ARMv7 now, so
make PSCI as the only way for the SMP boot protocol before some updates
for the ACPI spec or the Parking protocol spec.

ACPI only supports PSCI 0.2+, since prior to PSCI 0.2 function IDs are
not well-defined.

Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Parth Dixit <parth.dixit@linaro.org>
Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>