xillybus: XILLYBUS_OF should depend on HAS_DMA

If NO_DMA=y:

    drivers/built-in.o: In function `xilly_of_unmap':
    xillybus_of.c:(.text+0xa860e): undefined reference to `dma_unmap_single'
    drivers/built-in.o: In function `xilly_map_single_of':
    xillybus_of.c:(.text+0xa8668): undefined reference to `dma_map_single'
    xillybus_of.c:(.text+0xa8676): undefined reference to `dma_mapping_error'
    xillybus_of.c:(.text+0xa86ca): undefined reference to `dma_unmap_single'
    drivers/built-in.o: In function `xilly_dma_sync_single_for_device_of':
    xillybus_of.c:(.text+0xa8700): undefined reference to `dma_sync_single_for_cpu'
    drivers/built-in.o: In function `xilly_dma_sync_single_for_cpu_of':
    xillybus_of.c:(.text+0xa8726): undefined reference to `dma_sync_single_for_cpu'

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Eli Billauer <eli.billauer@gmail.com>
--
v2:
  - Add Acked-by, send to char and misc drivers maintainers.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>