tty/serial: Migrate sa1100 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: NDmitry Safonov <dima@arista.com>
Link: https://lore.kernel.org/r/20191213000657.931618-37-dima@arista.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sa1100.c

@@ -7,10 +7,6 @@
  *  Copyright (C) 2000 Deep Blue Solutions Ltd.
  */
 
-#if defined(CONFIG_SERIAL_SA1100_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
-#define SUPPORT_SYSRQ
-#endif
-
 #include <linux/module.h>
 #include <linux/ioport.h>
 #include <linux/init.h>
@@ -214,9 +210,7 @@ sa1100_rx_chars(struct sa1100_port *sport)
 			else if (status & UTSR1_TO_SM(UTSR1_FRE))
 				flg = TTY_FRAME;
 
-#ifdef SUPPORT_SYSRQ
 			sport->port.sysrq = 0;
-#endif
 		}
 
 		if (uart_handle_sysrq_char(&sport->port, ch))
@@ -860,6 +854,7 @@ static int sa1100_serial_resume(struct platform_device *dev)
 static int sa1100_serial_add_one_port(struct sa1100_port *sport, struct platform_device *dev)
 {
 	sport->port.dev = &dev->dev;
+	sport->port.has_sysrq = IS_ENABLED(CONFIG_SERIAL_SA1100_CONSOLE);
 
 	// mctrl_gpio_init() requires that the GPIO driver supports interrupts,
 	// but we need to support GPIO drivers for hardware that has no such