ARM64 / ACPI: Enable ARM64 in Kconfig

Add Kconfigs to build ACPI on ARM64, and make ACPI available on ARM64.

acpi_idle driver is x86/IA64 dependent now, so make CONFIG_ACPI_PROCESSOR
depend on X86 || IA64, and implement it on ARM64 in the future.

CC: Rafael J. Wysocki <rjw@rjwysocki.net>
CC: Catalin Marinas <catalin.marinas@arm.com>
CC: Will Deacon <will.deacon@arm.com>
Reviewed-by: Grant Likely <grant.likely@linaro.org>
Tested-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Tested-by: Yijing Wang <wangyijing@huawei.com>
Tested-by: Mark Langsdorf <mlangsdo@redhat.com>
Tested-by: Jon Masters <jcm@redhat.com>
Tested-by: Timur Tabi <timur@codeaurora.org>
Tested-by: Robert Richter <rrichter@cavium.com>
Acked-by: Robert Richter <rrichter@cavium.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Graeme Gregory <graeme.gregory@linaro.org>
Signed-off-by: Al Stone <al.stone@linaro.org>
Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>