serial: port: Add support of PNP IRQ to __uart_read_properties()

The function __uart_read_properties doesn't cover PNP devices, so add IRQ
processing for PNP devices in the branch.

Signed-off-by: Guanbing Huang <albanhuang@tencent.com>
Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Bing Fan <tombinfan@tencent.com>
Tested-by: Linheng Du <dylanlhdu@tencent.com>
Link: https://lore.kernel.org/r/7f4ca31ef1cab4c6ecad22fafd82117686b696be.1713234515.git.albanhuang@tencent.com


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