tty/serial: Migrate imx 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: Fabio Estevam <[e-mail]>
Cc: NXP Linux Team <[e-mail]>
Cc: Pengutronix Kernel Team <[e-mail]>
Cc: Sascha Hauer <[e-mail]>
Cc: Shawn Guo <[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/imx.c

···
  * Copyright (C) 2004 Pengutronix
  */
 
-#if defined(CONFIG_SERIAL_IMX_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
-#define SUPPORT_SYSRQ
-#endif
-
 #include <linux/module.h>
 #include <linux/ioport.h>
 #include <linux/init.h>
···
 			if (rx & URXD_OVRRUN)
 				flg = TTY_OVERRUN;
 
-#ifdef SUPPORT_SYSRQ
 			sport->port.sysrq = 0;
-#endif
 		}
 
 		if (sport->port.ignore_status_mask & URXD_DUMMY_READ)
···
 	sport->port.iotype = UPIO_MEM;
 	sport->port.irq = rxirq;
 	sport->port.fifosize = 32;
+	sport->port.has_sysrq = IS_ENABLED(CONFIG_SERIAL_IMX_CONSOLE);
 	sport->port.ops = &imx_uart_pops;
 	sport->port.rs485_config = imx_uart_rs485_config;
 	sport->port.flags = UPF_BOOT_AUTOCONF;