siemens,am33x,rastaban: add rastaban config

rastaban is a draco version with more flash, more RAM
and faster CPU. Number of partitions is the same but
rootfs partition is different.

Signed-off-by: Samuel Egli <samuel.egli@siemens.com>
Acked-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>