tty/serial: Migrate clps711x 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: Alexander Shiyan <[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/clps711x.c

···
  *  Copyright (C) 2000 Deep Blue Solutions Ltd.
  */
 
-#if defined(CONFIG_SERIAL_CLPS711X_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
-#define SUPPORT_SYSRQ
-#endif
-
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/console.h>
···
 	s->port.mapbase		= res->start;
 	s->port.type		= PORT_CLPS711X;
 	s->port.fifosize	= 16;
+	s->port.has_sysrq	= IS_ENABLED(CONFIG_SERIAL_CLPS711X_CONSOLE);
 	s->port.flags		= UPF_SKIP_TEST | UPF_FIXED_TYPE;
 	s->port.uartclk		= clk_get_rate(uart_clk);
 	s->port.ops		= &uart_clps711x_ops;