tty/serial: Migrate sprd_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: Baolin Wang <baolin.wang7@gmail.com>
Cc: Orson Zhai <orsonzhai@gmail.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Acked-by: Chunyan Zhang <zhang.lyra@gmail.com>
Link: https://lore.kernel.org/r/20191213000657.931618-43-dima@arista.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sprd_serial.c

@@ -3,10 +3,6 @@
  * Copyright (C) 2012-2015 Spreadtrum Communications Inc.
  */
 
-#if defined(CONFIG_SERIAL_SPRD_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
-#define SUPPORT_SYSRQ
-#endif
-
 #include <linux/clk.h>
 #include <linux/console.h>
 #include <linux/delay.h>
@@ -1227,6 +1223,7 @@ static int sprd_probe(struct platform_device *pdev)
 	up->fifosize = SPRD_FIFO_SIZE;
 	up->ops = &serial_sprd_ops;
 	up->flags = UPF_BOOT_AUTOCONF;
+	up->has_sysrq = IS_ENABLED(CONFIG_SERIAL_SPRD_CONSOLE);
 
 	ret = sprd_clk_init(up);
 	if (ret)