i2c: emev2: add driver

Add a basic driver for the Renesas EMEV2 SoC. Based on the driver from
the BSP which was first worked on by Ian, and made ready for upstream by
me.

Signed-off-by: Ian Molton <ian.molton@codethink.co.uk>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>