log: Add a console driver

It is useful to display log messages on the console. Add a simple driver
to handle this.

Note that this driver outputs to the console, which may be serial or
video. It does not specifically select serial output.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

common/log_console.c

@@ -0,0 +1,23 @@
+/*
+ * Logging support
+ *
+ * Copyright (c) 2017 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <log.h>
+
+static int log_console_emit(struct log_device *ldev, struct log_rec *rec)
+{
+	puts(rec->msg);
+
+	return 0;
+}
+
+LOG_DRIVER(console) = {
+	.name	= "console",
+	.emit	= log_console_emit,
+};