m68k: add support for DMA_BIDIRECTIONAL in dma support functions

The dma cache support functions do not currently support the direction flag
DMA_BIDIRECTIONAL. If a driver passes this direction to dma_map_single or
friends you will get console output like this:

  dma_sync_single_for_device: unsupported dir 0

For example when using the Intel e100 ethernet driver on a ColdFire platform
with PCI bus. You will get a stream of these messages coming out.

Modify the dma cache support code adding support for DMA_BIDIRECTIONAL. It is
actioned by doing a cache push operation.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>

arch/m68k/kernel/dma.c

@@ -105,6 +105,7 @@ void dma_sync_single_for_device(struct device *dev, dma_addr_t handle,
 				size_t size, enum dma_data_direction dir)
 {
 	switch (dir) {
+	case DMA_BIDIRECTIONAL:
 	case DMA_TO_DEVICE:
 		cache_push(handle, size);
 		break;