Use a command group 'usb_blaster' with subcommands instead of individual
commands with 'usb_blaster_' prefix.
The old commands are still available for backward compatibility but
marked as deprecated.
Change-Id: I2ae3d96ba864c20d7db67c74677781a62bfc4eb5
Signed-off-by: Marc Schink <dev@zapb.de>
Reviewed-on: http://openocd.zylin.com/6407
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>