ACPI: processor: Remove unused empty stubs of some functions

ACPI: processor: Remove unused empty stubs of some functions

Empty stubs are defined in processor.h for some functions provided by
the ACPI processor idle driver, but those functions are only used in
the main ACPI processor driver which requires the ACPI processor idle
driver to be present (selecting CONFIG_ACPI_PROCESSOR causes
CONFIG_ACPI_PROCESSOR_IDLE to be selected too automatically).

This means that the empty stubs in question are not really necessary and
if both CONFIG_ACPI_PROCESSOR and CONFIG_ACPI_PROCESSOR_IDLE are unset,
the compiler complains that they are defined, but not used.  Drop them
to get rid of the compiler warning.

Signed-off-by: Huisong Li <lihuisong@huawei.com>
Link: https://patch.msgid.link/20250911112408.1668431-2-lihuisong@huawei.com
[ rjw: Subject and changelog rewrite ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>