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>

plat/imx/common/imx_uart_console.S

 /*
- * 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
  */
@@ -16,10 +16,11 @@
 #define UTS   0xb4 /* UART Test Register (mx31) */
 #define  URXD_RX_DATA    (0xFF)
 
-	.globl	console_uart_register
-	.globl	console_uart_init
-	.globl	console_uart_putc
-	.globl	console_uart_getc
+	.globl	console_imx_uart_register
+	.globl	console_imx_uart_init
+	.globl	console_imx_uart_putc
+	.globl	console_imx_uart_getc
+	.globl	console_imx_uart_flush
 
 func console_imx_uart_register
 	mov	x7, x30
@@ -32,7 +33,7 @@ func console_imx_uart_register
 
 	mov	x0, x6
 	mov	x30, x7
-	finish_console_register imx_uart putc=1, getc=1
+	finish_console_register imx_uart putc=1, getc=1, flush=1
 
 register_fail:
 	ret	x7
@@ -82,3 +83,8 @@ getc_error:
 	mov	w0, #-1
 	ret
 endfunc console_imx_uart_getc
+
+func console_imx_uart_flush
+	mov	x0, #0
+	ret
+endfunc console_imx_uart_flush

plat/imx/common/include/imx_uart.h

 /*
- * 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
  */
@@ -16,7 +16,7 @@ typedef struct {
 	uintptr_t base;
 } console_uart_t;
 
-int console_uart_register(uintptr_t baseaddr, uint32_t clock, uint32_t baud,
+int console_imx_uart_register(uintptr_t baseaddr, uint32_t clock, uint32_t baud,
 			   console_uart_t *console);
 #endif /*__ASSEMBLY__*/
 

plat/imx/imx8m/imx8mq/imx8mq_bl31_setup.c

 /*
- * 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 @@ void bl31_early_platform_setup2(u_register_t arg0, u_register_t arg1,
 #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
 	/*