NXP: Enable I2C for imx6sx

This commit add support for i2c on imx6sx.
I2C support is based on imx7d and requires NXP HAL.
The Device Tree binding is also changed to better reflect that i2c
driver support both imx6sx and imx7d.

Signed-off-by: Antonio Tessarolo <anthonytexdev@gmail.com>