i2c: iproc: Add Broadcom iProc I2C Driver

Add initial support to the Broadcom iProc I2C controller found in the
iProc family of SoCs.

The iProc I2C controller has separate internal TX and RX FIFOs, each has
a size of 64 bytes. The iProc I2C controller supports two bus speeds
including standard mode (100kHz) and fast mode (400kHz)

Signed-off-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Reviewed-by: Kevin Cernekee <cernekee@chromium.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>