powerpc/pmap: Convert all PowerPC pmaps to use IFUNCs instead of kobj

[jhibbits]

Summary

Since we have ifuncs in kernel now, use them for pmap, instead of our
poor-man's version of singleton kobjs. At the very least, this saves
one extra register stomp in the KPIs.

[jhibbits]

Fix bugs caused by my misunderstanding of how ifuncs work.

[jhibbits]

Apply to ps3.

[bdragon]

After a couple of days of debugging stuff to fix unrelated problems:

works on powerpc AIM32 (PowerPC G4)
works on powerpcspe (e500v2)
works on powerpc64 Book-E (e5500)

Have not tested AIM64 yet.

[bdragon]

Tested in AIM64 (in my superglue branch, but should be a valid test anyway)

Also gave it a couple of skims through.

[jhibbits]

Committed as r361544.