KVM: riscv: selftests: sv39 support needed?

[wu.fei9 at sanechips.com.cn]

I was running kvm selftests on qemu-system-riscv64 with "-cpu rva23s64", which
uses sv39 by default, then I got the following error. After some debugging I
found sv39 is not supported for selftests, should we add sv39 support? I can
prepare a patch if it's needed.

# ./arch_timer
Random seed: 0x6b8b4567
==== Test Assertion Failure ====
  arch_timer.c:73: false
  pid=144 tid=146 errno=0 - Success

Regards,
Fei.