dmaengine: dw_dma: add Device Tree probing capability

SPEAr platforms now support DT and so must convert all drivers to support DT.
This patch adds DT probing support for Synopsys DMA controller and updates its
documentation too.
Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>

Documentation/devicetree/bindings/dma/snps-dma.txt

+* Synopsys Designware DMA Controller
+
+Required properties:
+- compatible: "snps,dma-spear1340"
+- reg: Address range of the DMAC registers
+- interrupt-parent: Should be the phandle for the interrupt controller
+  that services interrupts for this device
+- interrupt: Should contain the DMAC interrupt number
+
+Example:
+
+	dma@fc000000 {
+		compatible = "snps,dma-spear1340";
+		reg = <0xfc000000 0x1000>;
+		interrupt-parent = <&vic1>;
+		interrupts = <12>;
+	};

drivers/dma/dw_dmac.c

@@ -17,6 +17,7 @@
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
+#include <linux/of.h>
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
@@ -1592,12 +1593,21 @@ static const struct dev_pm_ops dw_dev_pm_ops = {
 	.poweroff_noirq = dw_suspend_noirq,
 };
 
+#ifdef CONFIG_OF
+static const struct of_device_id dw_dma_id_table[] = {
+	{ .compatible = "snps,dma-spear1340" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, dw_dma_id_table);
+#endif
+
 static struct platform_driver dw_driver = {
 	.remove		= __exit_p(dw_remove),
 	.shutdown	= dw_shutdown,
 	.driver = {
 		.name	= "dw_dmac",
 		.pm	= &dw_dev_pm_ops,
+		.of_match_table = of_match_ptr(dw_dma_id_table),
 	},
 };