Move debug and logging support to a separate header

Before adding new features, move these definitions to a separate header
to avoid further cluttering common.h.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/include/log.h b/include/log.h
new file mode 100644
index 0000000..08ad44c
--- /dev/null
+++ b/include/log.h
@@ -0,0 +1,59 @@
+/*
+ * Logging support
+ *
+ * Copyright (c) 2017 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __LOG_H
+#define __LOG_H
+
+#ifdef DEBUG
+#define _DEBUG	1
+#else
+#define _DEBUG	0
+#endif
+
+#ifdef CONFIG_SPL_BUILD
+#define _SPL_BUILD	1
+#else
+#define _SPL_BUILD	0
+#endif
+
+/*
+ * Output a debug text when condition "cond" is met. The "cond" should be
+ * computed by a preprocessor in the best case, allowing for the best
+ * optimization.
+ */
+#define debug_cond(cond, fmt, args...)			\
+	do {						\
+		if (cond)				\
+			printf(pr_fmt(fmt), ##args);	\
+	} while (0)
+
+/* Show a message if DEBUG is defined in a file */
+#define debug(fmt, args...)			\
+	debug_cond(_DEBUG, fmt, ##args)
+
+/* Show a message if not in SPL */
+#define warn_non_spl(fmt, args...)			\
+	debug_cond(!_SPL_BUILD, fmt, ##args)
+
+/*
+ * An assertion is run-time check done in debug mode only. If DEBUG is not
+ * defined then it is skipped. If DEBUG is defined and the assertion fails,
+ * then it calls panic*( which may or may not reset/halt U-Boot (see
+ * CONFIG_PANIC_HANG), It is hoped that all failing assertions are found
+ * before release, and after release it is hoped that they don't matter. But
+ * in any case these failing assertions cannot be fixed with a reset (which
+ * may just do the same assertion again).
+ */
+void __assert_fail(const char *assertion, const char *file, unsigned int line,
+		   const char *function);
+#define assert(x) \
+	({ if (!(x) && _DEBUG) \
+		__assert_fail(#x, __FILE__, __LINE__, __func__); })
+
+#endif