i2c: iproc: add NIC I2C support

Add NIC I2C support to the iProc I2C driver. Access to the NIC I2C base
registers requires going through the IDM wrapper to map into the NIC's
address space

Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>
Signed-off-by: Ray Jui <ray.jui@broadcom.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>