riscv: fu540: Use correct API to get L2 cache controller base address

At present fdtdec_get_addr() is used to get L2 cache controller base
address. This only works for a fixed #address-cells and #size-cells.
Change to use fdtdec_get_addr_size_auto_parent() instead.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Rick Chen <rick@andestech.com>
Reviewed-by: Pragnesh Patel <pragnesh.patel@openfive.com>