There are several IOMMU allocator bugs.  Instead of trying to fix this
overly complicated code, just mirror the PCI IOMMU arena allocator
which is very stable and well stress tested.

I tried to make the code as identical as possible so we can switch
sun4u PCI and SBUS over to a common piece of IOMMU code.  All that
will be need are two callbacks, one to do a full IOMMU flush and one
to do a streaming buffer flush.

This patch gets rid of a lot of hangs and mysterious crashes on SBUS
sparc64 systems, at least for me.
Signed-off-by: David S. Miller <davem@davemloft.net>