This patch converts the old method of creating a list of command
onto the new LG-arrays code. The old u_boot_cmd section is converted
to new u_boot_list_cmd subsection and LG-array macros used as needed.

Minor adjustments had to be made to the common code to work with the
LG-array macros, mostly the fixup_cmdtable() calls are now passed the
ll_entry_start and ll_entry_count instead of linker-generated symbols.

The command.c had to be adjusted as well so it would use the newly
introduced LG-array API instead of directly using linker-generated
symbols.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Joe Hershberger <joe.hershberger@gmail.com>
Cc: Mike Frysinger <vapier@gentoo.org>