tty/serial: Migrate efm32-uart 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: "Uwe Kleine-König" <[e-mail]>
Cc: Pengutronix Kernel Team <[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/efm32-uart.c

···
 // SPDX-License-Identifier: GPL-2.0
-#if defined(CONFIG_SERIAL_EFM32_UART_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
-#define SUPPORT_SYSRQ
-#endif
-
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/io.h>
···
 	efm_port->port.type = PORT_EFMUART;
 	efm_port->port.iotype = UPIO_MEM32;
 	efm_port->port.fifosize = 2;
+	efm_port->port.has_sysrq = IS_ENABLED(CONFIG_SERIAL_EFM32_UART_CONSOLE);
 	efm_port->port.ops = &efm32_uart_pops;
 	efm_port->port.flags = UPF_BOOT_AUTOCONF;