i2c: iproc: use wrapper for read/write access

Use the following wrapper for read/write access of iProc i2c registers:
u32 iproc_i2c_rd_reg(struct bcm_iproc_i2c_dev *iproc_i2c,
                     u32 offset)
void iproc_i2c_wr_reg(struct bcm_iproc_i2c_dev *iproc_i2c, u32 offset,
                      u32 val)

This preps the driver for support of indirect register access required
by certain SoCs with this iProc I2C block integrated

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>