media: staging: tegra-vde: select DMA_SHARED_BUFFER

Without CONFIG_DMA_SHARED_BUFFER we run into a link error for the
dma_buf_* APIs:

ERROR: "dma_buf_map_attachment" [drivers/staging/media/tegra-vde/tegra-vde.ko] undefined!
ERROR: "dma_buf_attach" [drivers/staging/media/tegra-vde/tegra-vde.ko] undefined!
ERROR: "dma_buf_get" [drivers/staging/media/tegra-vde/tegra-vde.ko] undefined!
ERROR: "dma_buf_put" [drivers/staging/media/tegra-vde/tegra-vde.ko] undefined!
ERROR: "dma_buf_detach" [drivers/staging/media/tegra-vde/tegra-vde.ko] undefined!
ERROR: "dma_buf_unmap_attachment" [drivers/staging/media/tegra-vde/tegra-vde.ko] undefined!

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>