[RFC] Deprecate AGP GART support for Radeon/Nouveau/TTM

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Unfortunately AGP is still to widely used as we could just drop support for using its GART.

Not using the AGP GART also doesn't mean a loss in functionality since drivers will just fallback to the driver specific PCI GART.

For now just deprecate the code and don't enable the AGP GART in TTM even when general AGP support is available.

Please comment,
Christian.