ACPI: LPSS: Remove nested ifdeffery for CONFIG_PM

There is no need to have the ifdef CONFIG_PM to be nested.
The second and so on will obviously become a no-op.

Remove redundant nested ifdeffery.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>