Due to clock stretch, our HW IP cannot meet the ac-timing
spec(tSU;STA,tSU;STO). 
There isn't a same delay for clock stretching, so we need pass a
parameter which can be found through measurement to meet most
conditions.

What about using this existing binding?

- i2c-scl-internal-delay-ns
        Number of nanoseconds the IP core additionally needs to setup SCL.