serial: 8250_dw: Sort headers alphabetically

For the sake of better maintenance, sort included headers alphabetically.
While at it, split the serial group of headers which makes clear the
subsystem the driver belongs to.

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220630093816.28271-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>