i2c: Add Spreadtrum I2C controller driver

This patch adds the I2C controller driver for Spreadtrum SC9860 platform.

Signed-off-by: Baolin Wang <baolin.wang@spreadtrum.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>