Commands are added to U-Boot by creating a new command structure.
  This is done by first including command.h
  
  Then using the U_BOOT_CMD() macro to fill in a cmd_tbl_t struct.
  
  U_BOOT_CMD(name,maxargs,repeatable,command,"usage","help")
  
  name:	 is the name of the commad. THIS IS NOT a string.
  maxargs: the maximumn numbers of arguments this function takes
  command: Function pointer (*cmd)(struct cmd_tbl_s *, int, int, char *[]);
  usage:	 Short description. This is a string
  help:	 long description. This is a string
  
  
  **** Behinde the scene ******
  
  The structure created is named with a special prefix (__u_boot_cmd_)
  and placed by the linker in a special section.
  
  This makes it possible for the final link to extract all commands
  compiled into any object code and construct a static array so the
  command can be found in an array starting at __u_boot_cmd_start.
  
  If a new board is defined do not forget to define the command section
  by writing in u-boot.lds ($(TOPDIR)/board/boardname/u-boot.lds) these
  3 lines:
  
  	__u_boot_cmd_start = .;
  	.u_boot_cmd : { *(.u_boot_cmd) }
  	__u_boot_cmd_end = .;