caif: CAIF_VIRTIO should depend on HAS_DMA

caif: CAIF_VIRTIO should depend on HAS_DMA

If NO_DMA=y:

drivers/built-in.o: In function `cfv_destroy_genpool':
drivers/net/caif/caif_virtio.c:364: undefined reference to `dma_free_coherent'
drivers/built-in.o: In function `cfv_create_genpool':
drivers/net/caif/caif_virtio.c:397: undefined reference to `dma_alloc_coherent'

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Dmitry Tarnyagin <dmitry.tarnyagin@lockless.no>
Cc: David S. Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>