stm32mp1: update RCC binding after kernel realignment

RCC is no more a mfd and add a complete example
and alignment with lastest TF-A binding

Change-Id: Icb3a5f234a55e87e718a4e7cd2baea7cdbc80db0
Signed-off-by: Patrick Delaunay <[email protected]>
Reviewed-on: https://gerrit.st.com/116650
Reviewed-by: CIBUILD <[email protected]>
Reviewed-by: Nicolas LE BAYON <[email protected]>
Reviewed-by: CITOOLS <[email protected]>