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/Makefile b/cmd/Makefile
index 5ec2f9e..4998643 100644
--- a/cmd/Makefile
+++ b/cmd/Makefile
@@ -32,6 +32,7 @@
 obj-$(CONFIG_CMD_CACHE) += cache.o
 obj-$(CONFIG_CMD_CBFS) += cbfs.o
 obj-$(CONFIG_CMD_CLK) += clk.o
+obj-$(CONFIG_CMD_CLS) += cls.o
 obj-$(CONFIG_CMD_CONFIG) += config.o
 obj-$(CONFIG_CMD_CONITRACE) += conitrace.o
 obj-$(CONFIG_CMD_CONSOLE) += console.o