Port recent MAME ppc changes

[toxieainc]

Hi!

Just for tracking: Maybe some of the recent PPC fixes in MAME could make sense to be ported?

[dukeeeey]

Sure, what was fixed? :)

[toxieainc]

Its a rather long list, don't know though what exactly would apply to the PPC in Model 3? https://github.com/mamedev/mame/commits/master/src/devices/cpu/powerpc

While at it, SCSP also saw some updates: https://github.com/mamedev/mame/commits/master/src/devices/sound/scsp.cpp