tty: serial: 8250: add DFL bus driver for Altera 16550.

Add a Device Feature List (DFL) bus driver for the Altera
16550 implementation of UART.

Signed-off-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Marco Pagani <marpagan@redhat.com>
Link: https://lore.kernel.org/r/20230115151447.1353428-5-matthew.gerlach@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>