serial: sc16is7xx: hardware reset chip if reset-gpios is defined in DT

serial: sc16is7xx: hardware reset chip if reset-gpios is defined in DT

Some boards connect a GPIO to the reset pin, and the reset pin needs
to be set up correctly before accessing the chip.

Add a function to handle the chip reset. If the reset-gpios is defined
in the DT, do hardware reset through this GPIO, otherwise do software
reset as before.

Reviewed-by: Lech Perczak <lech.perczak@camlingroup.com>
Tested-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Reviewed-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Signed-off-by: Hui Wang <hui.wang@canonical.com>
Link: https://lore.kernel.org/r/20240618112620.152848-2-hui.wang@canonical.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>