Add minimal device tree data for Keystone2 based SOCs. Patch
contains mainly ARM related SOC data and nothing about EVM specific
yet.

Cc: Grant Likely <grant.likely@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: arm@kernel.org
Acked-by: NOlof Johansson <olof@lixom.net>
Signed-off-by: NSantosh Shilimkar <santosh.shilimkar@ti.com>