i2c: rename kirkwood_i2c to mvtwsi

This driver is not kirkwood-specific and can also be used
e.g. by orion5x. Rename to a SoC-neutral name.

Signed-off-by: Albert Aribaud <albert.aribaud@free.fr>
Acked-by: Prafulla <Wadaskar&lt;prafulla@marvell.com>
Acked-by: Heiko <Schocher&lt;hs@denx.de>