dt-bindings: i2c: i2c-davinci: Update binding for 66AK2Gx pwr dm property

Add pm-domains property which is required for 66AK2Gx. Also document 66AK2G
unique clocks property usage.

Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>