i2c-nomadik: add regulator support

This on-chip I2C controller needs to fetch the regulator
representing its voltage domain so that it won't be switched off.

Signed-off-by: Jonas Aberg <jonas.aberg@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>