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>

common/cmd_immap.c

@@ -615,39 +615,39 @@ do_mccinfo (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 U_BOOT_CMD(
 	siuinfo,	1,	1,	do_siuinfo,
 	"print System Interface Unit (SIU) registers",
-	NULL
+	""
 );
 
 U_BOOT_CMD(
 	memcinfo,	1,	1,	do_memcinfo,
 	"print Memory Controller registers",
-	NULL
+	""
 );
 
 U_BOOT_CMD(
 	sitinfo,	1,	1,	do_sitinfo,
 	"print System Integration Timers (SIT) registers",
-	NULL
+	""
 );
 
 #ifdef CONFIG_8260
 U_BOOT_CMD(
 	icinfo,	1,	1,	do_icinfo,
 	"print Interrupt Controller registers",
-	NULL
+	""
 );
 #endif
 
 U_BOOT_CMD(
 	carinfo,	1,	1,	do_carinfo,
 	"print Clocks and Reset registers",
-	NULL
+	""
 );
 
 U_BOOT_CMD(
 	iopinfo,	1,	1,	do_iopinfo,
 	"print I/O Port registers",
-	NULL
+	""
 );
 
 U_BOOT_CMD(
@@ -659,62 +659,61 @@ U_BOOT_CMD(
 U_BOOT_CMD(
 	dmainfo,	1,	1,	do_dmainfo,
 	"print SDMA/IDMA registers",
-	NULL
+	""
 );
 
 U_BOOT_CMD(
 	fccinfo,	1,	1,	do_fccinfo,
 	"print FCC registers",
-	NULL
+	""
 );
 
 U_BOOT_CMD(
 	brginfo,	1,	1,	do_brginfo,
 	"print Baud Rate Generator (BRG) registers",
-	NULL
+	""
 );
 
 U_BOOT_CMD(
 	i2cinfo,	1,	1,	do_i2cinfo,
 	"print I2C registers",
-	NULL
+	""
 );
 
 U_BOOT_CMD(
 	sccinfo,	1,	1,	do_sccinfo,
 	"print SCC registers",
-	NULL
+	""
 );
 
 U_BOOT_CMD(
 	smcinfo,	1,	1,	do_smcinfo,
 	"print SMC registers",
-	NULL
+	""
 );
 
 U_BOOT_CMD(
 	spiinfo,	1,	1,	do_spiinfo,
 	"print Serial Peripheral Interface (SPI) registers",
-	NULL
+	""
 );
 
 U_BOOT_CMD(
 	muxinfo,	1,	1,	do_muxinfo,
 	"print CPM Multiplexing registers",
-	NULL
+	""
 );
 
 U_BOOT_CMD(
 	siinfo,	1,	1,	do_siinfo,
 	"print Serial Interface (SI) registers",
-	NULL
+	""
 );
 
 U_BOOT_CMD(
 	mccinfo,	1,	1,	do_mccinfo,
 	"print MCC registers",
-	NULL
+	""
 );
 
-
 #endif