ARM: imx: add support code for IMX50 based machines

Add machine support code for the Freescale IMX50 SoC.

The IMX50 is quite similar to the Freescale IMX53, and contains many of the
same periperhal hardware modules, at the same address offsets as the IMX53.
(Notable exceptions are that the IMX50 contains no CAN bus hardware, less
GPIO, no VPU, it does contain an Electrophoretic display controller though).

This support code uses some of the IMX53 setup code to reduce duplication
of what would be identical init IO setup.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>