[RFC part1 PATCH 4/7] ARM64 / ACPI: Introduce the skeleton of _PDC related for ARM64

[One Thousand Gnomes]

O> +enum idle_boot_override { IDLE_NO_OVERRIDE = 0, IDLE_HALT, IDLE_NOMWAIT,
> +			IDLE_POLL, IDLE_FORCE_MWAIT };

This should probably move out of the arch directory to be a single enum
including both platforms values. That will make it rather easier to keep
sane and avoid ifdefs around which definitions are for which processor.