flexcan controller register

/*********************************************************************
 *                  flexcan controller register
 * 说明：
 *     由于设备树没有正确注册CAN控制器设备，导致内核没有生产CAN设备。
 * 另外就是在调试阶段可以make menuconfig加上can debug信息，如果需要
 * 内核支持vcan，也需要通过make menuconfig来对其进行支持。
 *
 *                                   2017-8-15 深圳 龙华樟坑村 曾剑锋
 ********************************************************************/

一、参考文档：
    1. device tree can controller status setting
        https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/net/can/c_can.txt
    2. fsl-flexcan.txt
        https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/net/can/fsl-flexcan.txt

二、处理方法：
    1. 设备树路径：arch/arm/boot/dts/imx6qdl.dtsi
        flexcan1: can@02090000 {
            compatible = "fsl,imx6q-flexcan";
            reg = <0x02090000 0x4000>;
            interrupts = <0 110 IRQ_TYPE_LEVEL_HIGH>;
            clocks = <&clks IMX6QDL_CLK_CAN1_IPG>,
                 <&clks IMX6QDL_CLK_CAN1_SERIAL>;
            clock-names = "ipg", "per";
            stop-mode = <&gpr 0x34 28 0x10 17>;
            status = "okay";    /* change disable to okay */
        };

        flexcan2: can@02094000 {
            compatible = "fsl,imx6q-flexcan";
            reg = <0x02094000 0x4000>;
            interrupts = <0 111 IRQ_TYPE_LEVEL_HIGH>;
            clocks = <&clks IMX6QDL_CLK_CAN2_IPG>,
                 <&clks IMX6QDL_CLK_CAN2_SERIAL>;
            clock-names = "ipg", "per";
            stop-mode = <&gpr 0x34 29 0x10 18>;
            status = "okay";    /* change disable to okay */
        };
    2. 查看CAN设备：
        root@freescale ~$ ifconfig -a
        can0      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
                  NOARP  MTU:16  Metric:1
                  RX packets:0 errors:0 dropped:0 overruns:0 frame:0
                  TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
                  collisions:0 txqueuelen:10
                  RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
                  Interrupt:142

        can1      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
                  NOARP  MTU:16  Metric:1
                  RX packets:0 errors:0 dropped:0 overruns:0 frame:0
                  TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
                  collisions:0 txqueuelen:10
                  RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
                  Interrupt:143
        ...
        root@freescale ~$