Add a check to make sure that the user's arguments actually find a board
in boards.cfg. Previously, if a user misspelled an argument the
argument would be discarded without warning. For example, running
'MAKEALL -c 85xx' with the intention of compiling all Freescale 85xx
boards would instead silently discard the '-c 85xx' argument since the
proper cpu name is 'mpc85xx' and then proceed to compile all PowerPC
boards (MAKEALL's default).
Also fix an unrelated typo.
Signed-off-by: Peter Tyser <email@example.com>