KVM: riscv: selftests: get-reg-list print_reg should never fail

When outputting the "new" register list we want to print all of the
new registers, decoding as much as possible of each of them. Also, we
don't want to assert while listing registers with '--list'. We output
"/* UNKNOWN */" after each new register (which we were already doing
for some), which should be enough.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Haibo Xu <haibo1.xu@intel.com>
Signed-off-by: Anup Patel <anup@brainfault.org>