ARM: dts: bcm23550: Add SoC-specific I2C compatible

Add BCM23550-specific compatible for brcm,kona-i2c nodes. While not
currently used by the i2c-bcm-kona driver, they can serve for further
customization, if required.
Done in preparation for dt-binding coversion to DT schema.

Signed-off-by: Stanislav Jakubek <stano.jakubek@gmail.com>
Link: https://lore.kernel.org/r/9875ec0211187e4f5e2a4379c63eacdb69b31d7a.1682252615.git.stano.jakubek@gmail.com


Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>