dma-buf: Display buffer name in debugfs

Now that the dma-buf buffer name is unique, display it for each buffer in
the dma-buf debugfs so that clients can easily identify which buffer is
being referred to.

Change-Id: I83db2dd385523db9c0df9360084c4f3d4a0571e4
Signed-off-by: Liam Mark <lmark@codeaurora.org>