log: Handle line continuation

When multiple log() calls are used which don't end in newline, the
log prefix is prepended multiple times in the same line. This makes the
output look strange.

Fix this by detecting when the previous log record did not end in newline.
In that case, setting a flag.

Drop the unused BUFFSIZE in the test while we are here.

As an example implementation, update log_console to check the flag and
produce the expected output.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/asm-generic/global_data.h

@@ -410,6 +410,12 @@ struct global_data {
 	 * This value is used as logging level for continuation messages.
 	 */
 	int logl_prev;
+	/**
+	 * @log_cont: Previous log line did not finished wtih \n
+	 *
+	 * This allows for chained log messages on the same line
+	 */
+	bool log_cont;
 #endif
 #if CONFIG_IS_ENABLED(BLOBLIST)
 	/**