ACPICA: Simplify configuration of global ACPI_REDUCED_HARDWARE macro.

Surround definition of this with a #ifndef so that the kernel
can define it elsewhere if desired.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>