The "DART" iommu used on Apple U3 chipset will appear into 3rd party
products soon, thus the code shouldn't be named "pmac_*" anymore.

Also, the explicit config option is no longer needed, there is no
reason to build a PowerMac kernel without the iommu support, and
it can always be disabled at runtime with a cmdline option for
testing or debugging.

This patch do the appropriate renaming and makes the config option
implicit & selected when pmac support is included.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>