cmd: add clear screen 'cls' command

Add common clear screen command for configurations
CONFIG_DM_VIDEO, CONFIG_LCD and CONFIG_CFB_CONSOLE.

Remove the existing cls command implementation from
lcd.c code and activate the command for all boards
enabling CONFIG_LCD for compatibility reasons.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Tested-by: Patrick.Delaunay <patrick.delaunay@free.fr>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index e2973b3..b1cd1c9 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1380,6 +1380,14 @@
 	  Enable the 'conitrace' command which displays the codes received
 	  from the console input as hexadecimal numbers.
 
+config CMD_CLS
+	bool "Enable clear screen command 'cls'"
+	depends on CFB_CONSOLE || DM_VIDEO || LCD || VIDEO
+	default y if LCD
+	help
+	  Enable the 'cls' command which clears the screen contents
+	  on video frame buffer.
+
 config CMD_DISPLAY
 	bool "Enable the 'display' command, for character displays"
 	help