ACPI: Move PRM config option under the main ACPI config

ACPI: Move PRM config option under the main ACPI config

Currently PRM(Platform Runtime Mechanism) config option is listed along
with the main ACPI (Advanced Configuration and Power Interface) option
at the same level. On ARM64 platforms unlike x86, ACPI option is listed
at the topmost level of configuration menu. It is rather very confusing
to see PRM option also listed along with ACPI in the topmost level.

Move the same under ACPI config option. No functional change, just changes
the level of visibility of this option under the configuration menu.

Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>