General help message cleanup

Many of the help messages were not really helpful; for example, many
commands that take no arguments would not print a correct synopsis
line, but "No additional help available." which is not exactly wrong,
but not helpful either.

Commit ``Make "usage" messages more helpful.'' changed this
partially. But it also became clear that lots of "Usage" and "Help"
messages (fields "usage" and "help" in struct cmd_tbl_s respective)
were actually redundant.

This patch cleans this up - for example:

Before:
	=> help dtt
	dtt - Digital Thermometer and Thermostat

	Usage:
	dtt         - Read temperature from digital thermometer and thermostat.

After:
	=> help dtt
	dtt - Read temperature from Digital Thermometer and Thermostat

	Usage:
	dtt

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/common/cmd_portio.c b/common/cmd_portio.c
index 41b1991..f8befee 100644
--- a/common/cmd_portio.c
+++ b/common/cmd_portio.c
@@ -94,7 +94,7 @@
 U_BOOT_CMD(
 	out,	3,	1,	do_portio_out,
 	"write datum to IO port",
-	"[.b, .w, .l] port value\n    - output to IO port\n"
+	"[.b, .w, .l] port value\n    - output to IO port"
 );
 
 int do_portio_in (cmd_tbl_t * cmdtp, int flag, int argc, char *argv[])
@@ -159,5 +159,5 @@
 	in,	2,	1,	do_portio_in,
 	"read data from an IO port",
 	"[.b, .w, .l] port\n"
-	"    - read datum from IO port\n"
+	"    - read datum from IO port"
 );