dhrystone: Fix documentation ...

BAREBOX_CMD_HELP_TEXT may not contain a linebreak.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

commands: Add dhrystone ...

This tool will help to measure the system performance.

Some SoCs haven't the possibility to route their clocks to the output pins.
So you can use dhrystone to get a feedback about the clock speed.

Signed-off-by: Daniel Schultz <d.schultz@phytec.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>