i2c: iproc: add polling support

Add polling support to the iProc I2C driver. Polling mode is
activated when the driver fails to obtain an interrupt ID from device
tree
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>