soc: add driver for the ARM RealView

This adds a SoC driver to be used by the ARM RealView
reference boards. We create the "versatile" directory to hold
the different ARM reference designs as per the pattern of the
clk directory layout. The driver utilze the syscon to get to
the register needed. After this we can use sysfs to get at
some SoC properties on RealView DT variants like this:

> cd /sysbus/soc/devices/soc0
> ls
board         family        machine       power         subsystem
build         fpga          manufacturer  soc_id        uevent
> cat family
Versatile
> cat fpga
Multi-layer AXI
> cat board
HBI-0147
> cat build
03

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Conflicts:
	drivers/soc/Kconfig
	drivers/soc/Makefile