arm, at91: generate boot.bin file for all atmel SoC

generate the boot.bin file for all atmel SoC (arm920, arm926, armv7)

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Andreas Bießmann <andreas.devel@googlemail.com>
Reviewed-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
[fix subject]
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>