We now have a branch that moves about a third of the header files from arch/arm/mach-*/ that are actually included by device drivers into the include/linux/platform_data directory, and this patch set has been met with general approval. It will probably create a number of trivial merge conflicts in v3.7-rc1, but it is a significant help on the way to avoid including mach headers in any drivers.
Some of the platform maintainers also managed to clean up their other header files during the hacking session that followed the discussion.