Avoid driver-specific AGP user-populated types, since we don't know what AGP

Avoid driver-specific AGP user-populated types, since we don't know what AGP
driver we're on.
Avoid global cache flushes before inserting pages.
In general, they are never mapped, and not accessed through the kernel map, so
a cache flush should not be necessary. The exception is pages that are bound
cached. We might need a cache flush for those.