tty/serial: Migrate vr41xx_siu to use has_sysrq

The SUPPORT_SYSRQ ifdeffery is not nice as:
- May create misunderstanding about sizeof(struct uart_port) between
different objects
- Prevents moving functions from serial_core.h
- Reduces readability (well, it's ifdeffery - it's hard to follow)

In order to remove SUPPORT_SYSRQ, has_sysrq variable has been added.
Initialise it in driver's probe and remove ifdeffery.

Signed-off-by: Dmitry Safonov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/vr41xx_siu.c

···
  *  Based on drivers/serial/8250.c, by Russell King.
  */
 
-#if defined(CONFIG_SERIAL_VR41XX_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
-#define SUPPORT_SYSRQ
-#endif
-
 #include <linux/console.h>
 #include <linux/errno.h>
 #include <linux/init.h>
···
 		port = &siu_uart_ports[i];
 		port->ops = &siu_uart_ops;
 		port->dev = &dev->dev;
+		port->has_sysrq = IS_ENABLED(CONFIG_SERIAL_VR41XX_CONSOLE);
 
 		retval = uart_add_one_port(&siu_uart_driver, port);
 		if (retval < 0) {