With the support of heterogeneous harts and PRCI model, it's now
possible to use the OpenSBI image (PLATFORM=sifive/fu540) built
for the real hardware.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>