serial: max3100: use new UPIO_BUS as iotype

Now that we have a new UPIO_BUS I/O type, use it to register our serial
port. This allows the driver to work properly when using DT where
membase/iobase are not set.

Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://patch.msgid.link/20260521-tty-upio-v3-10-bf74567994a0@dimonoff.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>