i2c: i2c-stm32: Add generic DMA API

This patch adds a generic DMA API to implement DMA support for i2c-stm32fx
drivers

Signed-off-by: M'boumba Cedric Madianga <cedric.madianga@gmail.com>
Signed-off-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>