riscv: sifive: fu540: enable all cache ways from U-Boot proper

Add L2 cache node to enable all cache ways from U-Boot proper.

Signed-off-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>