TH1520: broken CPU count detection

[Michael Opdenacker]

Greetings,

For the Yocto meta-riscv layer, we're trying to replace the downstream 
opensbi (called opensbi-revyos) by mainline opensbi:
https://github.com/riscv/meta-riscv/pull/685/

The board boots fine, but unfortunately, only 1 CPU core is detected. 
This surfaces in the Linux kernel log:

[    0.089851] smp: Bringing up secondary CPUs ...
[   10.165542] CPU1 failed to report alive state
[   20.241632] CPU2 failed to report alive state
[   30.316980] CPU3 failed to report alive state

Any tips for solving this issue?
Thanks in advance
Cheers
Michael