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/common.h b/arch/arm/mach-imx/common.h
index d019115..f9d0114 100644
--- a/arch/arm/mach-imx/common.h
+++ b/arch/arm/mach-imx/common.h
@@ -79,6 +79,7 @@
 void imx_set_soc_revision(unsigned int rev);
 unsigned int imx_get_soc_revision(void);
 void imx_init_revision_from_anatop(void);
+struct device *imx_soc_device_init(void);
 
 enum mxc_cpu_pwr_mode {
 	WAIT_CLOCKED,		/* wfi only */