Command usage cleanup

Remove command name from all command "usage" fields and update
common/command.c to display "name - usage" instead of
just "usage". Also remove newlines from command usage fields.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
diff --git a/common/cmd_df.c b/common/cmd_df.c
index c85b7a6..d64f900 100644
--- a/common/cmd_df.c
+++ b/common/cmd_df.c
@@ -33,5 +33,5 @@
 
 U_BOOT_CMD(
 	sf,	2,	1,	do_serial_flash,
-	"sf	- Serial flash sub-system\n",
+	"Serial flash sub-system",
 	"probe [bus:]cs		- init flash device on given SPI bus and CS\n")