drm/stm: drv: Improve data transfers

To optimize data transfers, align pitch on 128 bytes & height
on 4 bytes. This optimization is not applicable on hw without MMU.

Signed-off-by: Yannick Fertre <yannick.fertre@st.com>
Signed-off-by: Vincent Abriou <vincent.abriou@st.com>
Signed-off-by: Philippe Cornu <philippe.cornu@st.com>
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180130104200.21602-1-philippe.cornu@st.com