dma-buf: Make dma-buf anon file name unique

Making the dma-buf anon file name unique will allow clients to be able
to uniquely identify a dma-buf.

One advantage of this is that dma-buf memory leaks can be more easily
debugged as now we will be able to identify which dma-buf buffers a client
is using.

Change-Id: I5cff7baafdda16d2812201b73693fc32b38e86b4
Signed-off-by: Liam Mark <lmark@codeaurora.org>