The bootelf command could, but does not, pass additional arguments along
on the command line.  Make do_bootelf consume bootelf/flags/address as
needed and then pass along anything else to the ELF application we've
launched.

Reported-by: Thomas Doerfler <thomas.doerfler@embedded-brains.de>
Signed-off-by: Tom Rini <trini@konsulko.com>