DMA-BUF contiguous buffer physical address user-space exporter binding

Driver allowing user-space attaching of DMA-BUFs returning CPU physical
addresses. The reasoning for making this act like a regular device
described by DT is so the virtual device that binds the buffer can be
made to act as if it is out on a bus or behind an IOMMU, for example.

Required Properties:
 - compatible:		Must be "ti,dma_buf_phys"

Example:

dma_buf_phys {
	compatible = "ti,dma_buf_phys";
	iommus = <&some_iommu>;
	dma-coherent;
};
