ACPI / ARM64: Don't enable ACPI by default on ARM64

If ACPI is selectable it is enabled by default.  This is a good choice
for architectures where the overwhelming majority of systems use ACPI
like x86 and IA-64 but is less clear for architectures where it's less
common like ARM64.  Change the default selection so that it's only done
explicitly on those architectures where ACPI is universally used.

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: Olof Johansson <olof@lixom.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>