Add a simple allocator for DMA safe memory. It will provide contiguous
blocks of memory with D-Cache line size alignment.
NOTE: The optimal granule size is the D-Cache line size (64), but due
to restrictions in the granule allocator this would result in a maximum
block size of 2K only, thus use 256B granules instead givin 8K max block
size.
Once the granule allocator is fixed this limitation can be removed.
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