serial: 8250_pci: add Intel Tangier support

Intel Tangier contains 4 HSUART ports as found on Intel Edison board which are
8250 compatible. The patch adds necessary bits to the driver.

Note that the HSU port0 is currently unavailable and thus not supported.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>