ARM: keystone: Create new binding for K2G SoC

K2G SoC family is the newest version of the Keystone family of processors.

The technical reference manual for K2G can be found here:
http://www.ti.com/lit/ug/spruhy8/spruhy8.pdf



Add new bindings for K2G and the K2G evm. Also document these new bindings.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>