Driver for the native I2C adapter found in Rockchip RK3xxx SoCs.

Configuration is only possible through devicetree. The driver is
interrupt driven and supports the I2C_M_IGNORE_NAK mangling bit.
Signed-off-by: Max Schwarz <max.schwarz@online.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>