Fix clash between IH_ARCH_NDS32 and IH_ARCH_SANDBOX

NDS32 and SANDBOX architecture were sharing the same IH_ARCH number

Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Acked-by: Macpaul Lin <macpaul@andestech.com>
Acked-by: Marek Vasut <marek.vasut@gmail.com>