MXS: Implement DMA support into mxs-i2c

This patch implements DMA support into mxs-i2c. DMA transfers are now enabled
via DT. The DMA operation is enabled by default.
Signed-off-by: Marek Vasut <marex@denx.de>
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>

[wsa: rebased to 3.6-rc7]
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>

Documentation/devicetree/bindings/i2c/i2c-mxs.txt

@@ -6,6 +6,7 @@ Required properties:
 - interrupts: Should contain ERROR and DMA interrupts
 - clock-frequency: Desired I2C bus clock frequency in Hz.
                    Only 100000Hz and 400000Hz modes are supported.
+- fsl,i2c-dma-channel: APBX DMA channel for the I2C
 
 Examples:
 
@@ -16,4 +17,5 @@ i2c0: i2c@80058000 {
 	reg = <0x80058000 2000>;
 	interrupts = <111 68>;
 	clock-frequency = <100000>;
+	fsl,i2c-dma-channel = <6>;
 };

arch/arm/boot/dts/imx28.dtsi

@@ -661,6 +661,7 @@ i2c0: i2c@80058000 {
 				reg = <0x80058000 0x2000>;
 				interrupts = <111 68>;
 				clock-frequency = <100000>;
+				fsl,i2c-dma-channel = <6>;
 				status = "disabled";
 			};
 
@@ -671,6 +672,7 @@ i2c1: i2c@8005a000 {
 				reg = <0x8005a000 0x2000>;
 				interrupts = <110 69>;
 				clock-frequency = <100000>;
+				fsl,i2c-dma-channel = <7>;
 				status = "disabled";
 			};