Use a faster speed of 400 kbit/s for regular I2C busses.

Use a slower speed of 10 kbit/s for DDC/EDID to improve reliability.

Use a slower speed of 100 kbit/s for power I2C to be within specs of
the LM95245 temperature sensor.

While at it further annotate I2C pin usage.
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>