ARM: dts: add I2C device nodes for Broadcom Cygnus

Add I2C device nodes and its properties in bcm-cygnus.dtsi but keep
them disabled there. Individual I2C devices can be enabled in board
specific dts file when I2C slave devices are enabled in the future

Signed-off-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Reviewed-by: Kevin Cernekee <cernekee@chromium.org>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>