tty: serial: imx: fix link error with CONFIG_SERIAL_CORE_CONSOLE=n

aarch64-linux-gnu-ld: drivers/tty/serial/imx_earlycon.o: in function `imx_uart_console_early_write':
imx_earlycon.c:(.text+0x84): undefined reference to `uart_console_write'

The driver uses the uart_console_write(), but SERIAL_CORE_CONSOLE is not
selected, so uart_console_write is not defined, then we get the error.
Fix this by selecting SERIAL_CORE_CONSOLE.

Fixes: 699cc4df ("tty: serial: imx: add imx earlycon driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20200919063240.2754965-1-yangyingliang@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/Kconfig

@@ -521,6 +521,7 @@ config SERIAL_IMX_EARLYCON
 	depends on ARCH_MXC || COMPILE_TEST
 	depends on OF
 	select SERIAL_EARLYCON
+	select SERIAL_CORE_CONSOLE
 	help
 	  If you have enabled the earlycon on the Freescale IMX
 	  CPU you can make it the earlycon by answering Y to this option.