imx: make imx uart work for debug mode

With DEBUG_CONSOLE enabled, build will fail for imx8mq platform:

./build/imx8mq/release/bl31/imx8mq_bl31_setup.o:
In function `bl31_early_platform_setup2':
imx8mq_bl31_setup.c:(.text.bl31_early_platform_setup2+0x40):
	undefined reference to `console_uart_register'
Makefile:741: recipe for target 'build/imx8mq/release/bl31/bl31.elf' failed
make: *** [build/imx8mq/release/bl31/bl31.elf] Error 1

Besides, the .console_flush callback needs to be added to avoid
panic when debug mode is enabled, since the console_flush() will
call it without checking whether the function callback is valid.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
diff --git a/plat/imx/imx8m/imx8mq/imx8mq_bl31_setup.c b/plat/imx/imx8m/imx8mq/imx8mq_bl31_setup.c
index f4e6ee7..b18edd9 100644
--- a/plat/imx/imx8m/imx8mq/imx8mq_bl31_setup.c
+++ b/plat/imx/imx8m/imx8mq/imx8mq_bl31_setup.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2018-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -87,7 +87,7 @@
 #if DEBUG_CONSOLE
 	static console_uart_t console;
 
-	console_uart_register(IMX_BOOT_UART_BASE, IMX_BOOT_UART_CLK_IN_HZ,
+	console_imx_uart_register(IMX_BOOT_UART_BASE, IMX_BOOT_UART_CLK_IN_HZ,
 		IMX_CONSOLE_BAUDRATE, &console);
 #endif
 	/*