davinci_emac: fix for running with dcache enabled

DaVinci EMAC is present on TI AM35xx SoCs (ARMv7) which run with D-Cache
enabled by default. So we have to take care and flush/invalidate the
cache before/after the DMA operations.

Please note that the receive buffer alignment to 32 byte boundary comes
from the old driver version I don't know if it is really needed or
alignment to cache line size is enough.

Signed-off-by: Ilya Yanok <yanok@emcraft.com>
diff --git a/drivers/net/davinci_emac.h b/drivers/net/davinci_emac.h
index a42c93a..37c841c 100644
--- a/drivers/net/davinci_emac.h
+++ b/drivers/net/davinci_emac.h
@@ -24,8 +24,9 @@
 /* Ethernet Min/Max packet size */
 #define EMAC_MIN_ETHERNET_PKT_SIZE	60
 #define EMAC_MAX_ETHERNET_PKT_SIZE	1518
-/* 1518 + 18 = 1536 (packet aligned on 32 byte boundry) */
-#define EMAC_PKT_ALIGN			18
+/* Buffer size (should be aligned on 32 byte and cache line) */
+#define EMAC_RXBUF_SIZE	ALIGN(ALIGN(EMAC_MAX_ETHERNET_PKT_SIZE, 32),\
+				ARCH_DMA_MINALIGN)
 
 /* Number of RX packet buffers
  * NOTE: Only 1 buffer supported as of now