dt-bindings: soc: xilinx: Add support for K26 rev2 SOMs

Revision 2 is SW compatible with revision 1 but it is necessary to reflect
it in model and compatible properties which are parsed by user space.
Rev 2 has improved a power on boot reset and MIO34 shutdown glich
improvement done via an additional filter in the GreenPak chip.

Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/90e1a393154c3d87e8ee7dc9eef07fc937c1eaf7.1706019397.git.michal.simek@amd.com


Signed-off-by: Michal Simek <michal.simek@amd.com>