i2c: add support for Socionext SynQuacer I2C controller

This is a cleaned up version of the I2C controller driver for
the Fujitsu F_I2C IP, which was never supported upstream, and
has now been incorporated into the Socionext SynQuacer SoC.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
[wsa: updated MAINTAINERS entry and removed two empty lines]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>