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This will enable the elimination of a workaround in the USB driver that artifically allocates buffers twice as big as they need to be (which actually saves memory for very small buffers on the buggy platforms). When deciding how to allocate a dma buffer, armv4, armv6, mips, and x86/iommu all correctly check for the tag alignment <= maxsize as enabling simple uma/malloc based allocation. Powerpc, sparc64, x86/bounce, and arm64/bounce were all checking for alignment < maxsize; on those platforms when alignment was equal to the max size it would fall back to page-based allocators even for very small buffers. This change makes all platforms use the <= check. It should be noted that on all platforms other than arm[v6] and mips, this check is relying on undocumented behavior in malloc(9) that if you allocate a block of a given size it will be aligned to the next larger power-of-2 boundary. There is nothing in the malloc(9) man page that makes that explicit promise (but the busdma code has been relying on this behavior all along so I guess it works). Arm and mips code uses the allocator in kern/subr_busdma_buffalloc.c, which does explicitly implement this promise about size and alignment. Other platforms probably should switch to the aligned allocator.
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