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This is a complete redesign and rewrite of libbmm. This implementation
is based upon dma_bufs - where a dma_buf is a kernel-side buffer which
can be passed to and from other subsystems. libbmm becomes a provider
of dma_bufs - it permits userspace to allocate such things.
When a dma_buf is allocated, userspace is handed a file descriptor
which is unique to this buffer. This file descriptor can then be
passed into other subsystems, which can then request access to this
buffer.
The file descriptor supports very few operations - it can be mmap()d to
provide userspace access to the buffer, and it can be closed when it is
no longer required. Internally in the kernel, dma_bufs are reference
counted, so the dma_buf will only be freed when the last user gives up
its reference.
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