armv8: fsl-layerscape: spl: add debug UART support

To use the debug UART we have to call debug_uart_init() in the SPL. Do
so as soon as possible.

As an example, here is how you can use it on a LS1028A SoC:
CONFIG_DEBUG_UART=y
CONFIG_DEBUG_UART_BASE=0x21c0500
CONFIG_DEBUG_UART_CLOCK=200000000

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
diff --git a/arch/arm/cpu/armv8/fsl-layerscape/spl.c b/arch/arm/cpu/armv8/fsl-layerscape/spl.c
index d5131bc..888c02f 100644
--- a/arch/arm/cpu/armv8/fsl-layerscape/spl.c
+++ b/arch/arm/cpu/armv8/fsl-layerscape/spl.c
@@ -6,6 +6,7 @@
 #include <common.h>
 #include <clock_legacy.h>
 #include <cpu_func.h>
+#include <debug_uart.h>
 #include <env.h>
 #include <image.h>
 #include <init.h>
@@ -70,6 +71,8 @@
 	icache_enable();
 	/* Clear global data */
 	memset((void *)gd, 0, sizeof(gd_t));
+	if (IS_ENABLED(CONFIG_DEBUG_UART))
+		debug_uart_init();
 	board_early_init_f();
 	timer_init();
 #ifdef CONFIG_ARCH_LS2080A