microblaze: Add support for DMA_BIDIRECTIONAL

CDMA requires DMA_BIDIRECTIONAL option.

Signed-off-by: Michal Simek <monstr@monstr.eu>
diff --git a/arch/microblaze/kernel/dma.c b/arch/microblaze/kernel/dma.c
index 79c7465..393e6b2 100644
--- a/arch/microblaze/kernel/dma.c
+++ b/arch/microblaze/kernel/dma.c
@@ -26,6 +26,7 @@
 {
 	switch (direction) {
 	case DMA_TO_DEVICE:
+	case DMA_BIDIRECTIONAL:
 		flush_dcache_range(paddr + offset, paddr + offset + size);
 		break;
 	case DMA_FROM_DEVICE: