tty/serial: Migrate msm_serial 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.

Cc: Andy Gross <[e-mail]>
Cc: Bjorn Andersson <[e-mail]>
Cc: [e-mail]
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/msm_serial.c

···
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  */
 
-#if defined(CONFIG_SERIAL_MSM_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
-# define SUPPORT_SYSRQ
-#endif
-
 #include <linux/kernel.h>
 #include <linux/atomic.h>
 #include <linux/dma-mapping.h>
···
 	if (unlikely(irq < 0))
 		return -ENXIO;
 	port->irq = irq;
+	port->has_sysrq = IS_ENABLED(CONFIG_SERIAL_MSM_CONSOLE);
 
 	platform_set_drvdata(pdev, port);