MAKEALL: fix per arch board lists

MAKEALL: fix per arch board lists

The LIST_arm rule included the Atmel boards twice (by virtue of
including both LIST_at91 and LIST_ARM9) and was missing all the
arm720t, arm946es, and arm1176 boards.  Change this list to use
boards_by_arch() which is less error prone.  After this change
"./MAKEALL arm" and "./MAKEALL -a arm" build the same boards.

Also fix up some missing and duplicate boards to arm, mips, and m68k.

Signed-off-by: Allen Martin <amartin@nvidia.com>
Acked-by: Tom Rini <trini@ti.com>