ARM: mxs: Use soc bus infrastructure

Using the soc bus infrastructure is helpful for reporting several SoC related
information such as: family, machine, SoC name and SoC revision.

$ cat /sys/bus/soc/devices/soc0/family
Freescale MXS Family

$ cat /sys/bus/soc/devices/soc0/machine
Freescale i.MX28 Evaluation Kit

$ cat /sys/bus/soc/devices/soc0/soc_id
i.MX28

$ cat /sys/bus/soc/devices/soc0/revision
TO1.2

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>