dt-bindings: arm: fsl: Add PHYTEC i.MX6 UL/ULL devicetree bindings

Add devicetree bindings for i.MX6 UL/ULL based phyCORE-i.MX6 UL/ULL and
phyBOARD-Segin.

Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>