nds32: add support for leopard and orca board boot flow auto detect

hardware difference between leopard and orca as below:

flash setting     leoaprd     orca
bank size         32MB        64MB
bus width         32-bits     16-bits

Signed-off-by: rick <rick@andestech.com>
Signed-off-by: Kuan-Yu Kuo <ken.kuoky@gmail.com>