ACPI / scan: do not scan fixed hardware on HW-reduced platform

Fixed hardware does not exist on HW-reduced ACPI platforms since the
programming interface for them is not implemented on them, so no need
to scan that hardware on them.

This patch avoids creating the fixed power button ACPI device and
eliminates a probe error message from ACPI button driver on ASUS T100.

Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>