arm/acpi: Add acpi parameter to enable/disable acpi
Define new command line parameter "acpi" to enable/disable acpi.
This implements the following policy to decide whether ACPI should be
used to boot the system:
- acpi=off: ACPI will not be used to boot the system, even if there is
no alternative available (e.g., device tree is empty)
- acpi=force: only ACPI will be used to boot the system; if that fails,
there will be no fallback to alternative methods (such as device tree)
- otherwise, ACPI will be used as a fallback if the device tree turns
out to lack a platform description; the heuristic to decide this is
whether /chosen is the only node present at depth 1