[U-Boot] Logging SPL output with test/py

[Simon Glass]

Hi Stephen,

I'd like to get access to SPL output from a test. It seems that only
the output from U-Boot proper is logged, although I cannot see why.

For background, I have a new sandbox_spl target which includes SPL
code. I will likely merge it into the normal sandbox target...

It is definitely running SPL because I see the SPL console output when
I use the -s flag to test.py. But it does not appear in test-log.html.

Let me know if you have any ideas...

Thanks,
Simon