i2c: zx2967: add i2c controller driver for ZTE's zx2967 family

This patch adds i2c controller driver for ZTE's zx2967 family.

Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Jun Nie <jun.nie@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>