stm32mp1: Add image information for capsule updates

Enabling capsule update functionality on the platform requires
populating information on the images that are to be updated using the
functionality. Do so for the DK2 board.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Etienne Carriere <etienne.carriere@linaro.org>