ACPI: utils: Introduce helper for _DEP list lookup

The ACPI LPSS driver and the Surface platform driver code use almost the
same code pattern for checking if one ACPI device is present in the list
returned by _DEP for another ACPI device.

To reduce the resulting code duplication, introduce a helper for that
called acpi_device_dep() and invoke it from both places.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>