[PowerPC] INTRNG preparation: Rename our pic interface

[bdragon]

Summary

To allow for porting to the INTRNG framework, we need to be able to include the MI pic interface. Since we have an interface name conflict with it, we first have to change the name of ours.

Rename the powerpc pic interface to oldpic so they can coexist, and to help with spotting where code needs to be updated.
Update all pic interface calls in the PPC code.

Should be NFC.

[jhibbits]

Why not ppcpic, or similar?

[bdragon]

Well, because I'm planning on removing the interface once I have converted everything over to INTRNG.

Our pic interface does the same thing as intrng (and interrupt-related bits of the bus interface, like bus_config_intr).

If you feel strongly about it, yeah, I could certainly name it ppcpic instead, but I still think it would be better for it to go away once everything's working in INTRNG.

[bdragon]

I will be working on this offline in the background after reviewing the relevant past conversations.

[bdragon]

Abandoning this. will resubmit with the actual functionality later on if I ever get back to working on this one.