ARM: imx6: report soc info via soc device

The patch enables soc bus infrastructure and adds a function
imx_soc_device_init() to report soc info via soc device interface for
imx6qdl and imx6sl.  With the support, user space can get soc related
info by looking at sysfs like below.

  $ cat /sys/devices/soc0/machine
  Freescale i.MX6 Quad SABRE Smart Device Board
  $ cat /sys/devices/soc0/family
  Freescale i.MX
  $ cat /sys/devices/soc0/soc_id
  i.MX6Q
  $ cat /sys/devices/soc0/revision
  1.2

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
diff --git a/arch/arm/mach-imx/mxc.h b/arch/arm/mach-imx/mxc.h
index 8629e5b..99e03ea 100644
--- a/arch/arm/mach-imx/mxc.h
+++ b/arch/arm/mach-imx/mxc.h
@@ -34,6 +34,7 @@
 #define MXC_CPU_MX35		35
 #define MXC_CPU_MX51		51
 #define MXC_CPU_MX53		53
+#define MXC_CPU_IMX6SL		0x60
 #define MXC_CPU_IMX6DL		0x61
 #define MXC_CPU_IMX6Q		0x63