stm32mp1: Add clock and reset support

The clock driver is under dual license, BSD and GPLv2.
The clock driver uses device tree, so a minimal support for this is added.
The required files for driver and DTS files are in include/dt-bindings/.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Signed-off-by: Nicolas Le Bayon <nicolas.le.bayon@st.com>
Signed-off-by: Lionel Debieve <lionel.debieve@st.com>