exynos: Enable the debug UART in SPL

As a debugging aid, allow UART3 to be used as a debug UART in SPL. This
is a precursor to proper UART support, which requires a substantial
refactor.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/cpu/armv7/exynos/lowlevel_init.c b/arch/arm/cpu/armv7/exynos/lowlevel_init.c
index 120aaf8..3774607 100644
--- a/arch/arm/cpu/armv7/exynos/lowlevel_init.c
+++ b/arch/arm/cpu/armv7/exynos/lowlevel_init.c
@@ -25,6 +25,7 @@
 
 #include <common.h>
 #include <config.h>
+#include <debug_uart.h>
 #include <asm/arch/cpu.h>
 #include <asm/arch/dmc.h>
 #include <asm/arch/power.h>
@@ -216,6 +217,10 @@
 
 	if (actions & DO_CLOCKS) {
 		system_clock_init();
+#ifdef CONFIG_DEBUG_UART
+		exynos_pinmux_config(PERIPH_ID_UART3, PINMUX_FLAG_NONE);
+		debug_uart_init();
+#endif
 		mem_ctrl_init(actions & DO_MEM_RESET);
 		tzpc_init();
 	}