tty/serial: Migrate apbuart 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 <dima@arista.com>
Link: https://lore.kernel.org/r/20191213000657.931618-11-dima@arista.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/apbuart.c

@@ -11,10 +11,6 @@
  *  Copyright (C) 2009 Kristoffer Glembo <kristoffer@gaisler.com>, Aeroflex Gaisler AB
  */
 
-#if defined(CONFIG_SERIAL_GRLIB_GAISLER_APBUART_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
-#define SUPPORT_SYSRQ
-#endif
-
 #include <linux/module.h>
 #include <linux/tty.h>
 #include <linux/tty_flip.h>
@@ -626,6 +622,7 @@ static int __init grlib_apbuart_configure(void)
 		port->irq = 0;
 		port->iotype = UPIO_MEM;
 		port->ops = &grlib_apbuart_ops;
+		port->has_sysrq = IS_ENABLED(CONFIG_SERIAL_GRLIB_GAISLER_APBUART_CONSOLE);
 		port->flags = UPF_BOOT_AUTOCONF;
 		port->line = line;
 		port->uartclk = *freq_hz;