aspeed: Add AST2600 (BMC) to fby35

aspeed: Add AST2600 (BMC) to fby35

You can test booting the BMC with both '-device loader' and '-drive
file'. This is necessary because of how the fb-openbmc boot sequence
works (jump to 0x20000000 after U-Boot SPL).

    wget https://github.com/facebook/openbmc/releases/download/openbmc-e2294ff5d31d/fby35.mtd
    qemu-system-arm -machine fby35 -nographic \
        -device loader,file=fby35.mtd,addr=0,cpu-num=0 -drive file=fby35.mtd,format=raw,if=mtd

Signed-off-by: Peter Delevoryas <peter@pjd.dev>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20220705191400.41632-7-peter@pjd.dev>
Signed-off-by: Cédric Le Goater <clg@kaod.org>