log: Add a 'log level' command

Add a command for adjusting the log level.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 5a6afab..b745a7e 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1502,6 +1502,13 @@
 	  single-stepping, inspecting variables, etc. This is supported only
 	  on PowerPC at present.
 
+config CMD_LOG
+	bool "log - Generation, control and access to logging"
+	help
+	  This provides access to logging features. It allows the output of
+	  log data to be controlled to a limited extent (setting up the default
+	  maximum log level for emitting of records).
+
 config CMD_TRACE
 	bool "trace - Support tracing of function calls and timing"
 	help