ioat3: enable dca for completion writes

Tag completion writes for direct cache access to reduce the latency of
checking for descriptor completions.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/dma/ioat/registers.h b/drivers/dma/ioat/registers.h
index 85d04b8..97d26ea 100644
--- a/drivers/dma/ioat/registers.h
+++ b/drivers/dma/ioat/registers.h
@@ -84,6 +84,7 @@
 /* DMA Channel Registers */
 #define IOAT_CHANCTRL_OFFSET			0x00	/* 16-bit Channel Control Register */
 #define IOAT_CHANCTRL_CHANNEL_PRIORITY_MASK	0xF000
+#define IOAT3_CHANCTRL_COMPL_DCA_EN		0x0200
 #define IOAT_CHANCTRL_CHANNEL_IN_USE		0x0100
 #define IOAT_CHANCTRL_DESCRIPTOR_ADDR_SNOOP_CONTROL	0x0020
 #define IOAT_CHANCTRL_ERR_INT_EN		0x0010