ARM: dts: Add Calxeda ECX-2000 support

Separate out common dts pieces from highbank dts and add support for
Calxeda ECX-2000 (Midway) SOC.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>