i2c-nomadik: dynamic clocking

This makes sure the Nomadik I2C bus driver silicon is only clocked
when really needed, saving some microamps here and there when
there is no I2C traffic.

Acked-by: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
Signed-off-by: Sundar R Iyer <sundar.iyer@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>