arm64: defconfig: Enable ACPI

Enable ACPI by default to support testing of ACPI only systems and
ensure that defconfig will boot on anything, for arm64 this is not done
in Kconfig since a very large proportion of arm64 systems have no ACPI
at all.

Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Hanjun Guo <hanjun.guo@linaro.org>
Acked-by: Roy Franz <roy.franz@hpe.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>