serial: Add rs485_supported to uart_port

Preparing to move serial_rs485 struct sanitization into serial core,
each driver has to provide what fields/flags it supports. This
information is pointed into by rs485_supported.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220606100433.13793-4-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_core.c

@@ -1003,6 +1003,7 @@ int serial8250_register_8250_port(const struct uart_8250_port *up)
 		uart->port.throttle	= up->port.throttle;
 		uart->port.unthrottle	= up->port.unthrottle;
 		uart->port.rs485_config	= up->port.rs485_config;
+		uart->port.rs485_supported = up->port.rs485_supported;
 		uart->port.rs485	= up->port.rs485;
 		uart->rs485_start_tx	= up->rs485_start_tx;
 		uart->rs485_stop_tx	= up->rs485_stop_tx;

include/linux/serial_core.h

@@ -254,6 +254,7 @@ struct uart_port {
 	struct attribute_group	*attr_group;		/* port specific attributes */
 	const struct attribute_group **tty_groups;	/* all attributes (serial core use only) */
 	struct serial_rs485     rs485;
+	const struct serial_rs485	*rs485_supported;	/* Supported mask for serial_rs485 */
 	struct gpio_desc	*rs485_term_gpio;	/* enable RS485 bus termination */
 	struct serial_iso7816   iso7816;
 	void			*private_data;		/* generic platform data pointer */