roms/SLOF: crashes on G5 (970) with newer pseries

[Jake Hamby]

I've been testing QEMU + KVM-PR on a Power Mac G5 Quad, and it runs
better than I expected, but with a few glitches. The first one I
discovered: the SLOF ROM has been compiled for POWER7 or newer, and it
crashes when run on a G5 (KVM and TCG) if the pseries version is set
to 2.6 or higher. The xHCI SLOF driver crashes the guest with
pseries-2.6, and it doesn't even get to initializing the screen with
higher versions.

Fortunately, it was a small change to recompile SLOF from source with
the target set to "ppc970" instead of "ppcp7". I had to fix a few
build errors first. Commit link (I would paste the patches inline, but
I don't have Gmail set up for that yet):

https://github.com/jhamby/SLOF/commit/4ae9a012a2cec4a1b476c1b4a3933def5ae36f2b

And my commit to change the default QEMU board type to ppc970:

https://github.com/jhamby/SLOF/commit/619539cfa3a37f9527ae382cdb7573de7fa6d836

With these changes, the compiled slof.bin works perfectly for me with
pseries versions up to 4.2 (the highest version I tried that doesn't
expect CPU capabilities that the G5 doesn't have) and the 970mp CPU
type (with both KVM-PR and TCG).

I don't know if there are any negative performance implications of
compiling SLOF for PPC 970 and using it with later CPU types, but I'm
guessing that PowerNV is the preferred machine type for POWER8 and
newer now. It does feel like a bug that the SLOF ROM crashes
unexpectedly with older CPU models in legal machine configurations.

Regards,
Jake