serial: sc16is7xx: Add polling mode if no IRQ pin is available

Fall back to polling mode if no interrupt is configured because there
is no possibility to connect the interrupt pin.
If "interrupts" property is missing in devicetree the driver
uses a delayed worker to pull the state of interrupt status registers.

Signed-off-by: Andre Werner <andre.werner@systec-electronic.com>
Link: https://lore.kernel.org/r/20250110073104.1029633-2-andre.werner@systec-electronic.com


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