serial: 8250_dw: Add quirk for APM X-Gene SoC

The APM X-Gene SoC UART is the only board that still needs
the hard-coded values, so handle it separately in
dw8250_quirks(). The other ACPI platforms are able to
provide the values with device properties.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>