gpu: ion: Add support for sharing buffers with dma buf kernel handles

Currently ion can only share buffers with dma buf fd's. Fd's can not be
used inside the kernel as they are process specific so support for
sharing buffers with dma buf kernel handles is needed to support kernel
only use cases. An example use case could be a GPU driver using ion
that wants to share its output buffers with a 3d party display
controller driver supporting dma buf.

Change-Id: If1b3753ddbd5b44c5a3e622055d5473e16fc1c48
Signed-off-by: Johan Mossberg <johan.mossberg@stericsson.com>