stm32mp1: add dtbs rule for FIP package dependency

Because we are using firmware configuration in FIP
container, we must embed the corresponding device tree.

Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Change-Id: I2deae522f43086f884594d4dd78b053d3c08615e
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/182041


Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: Yann GAUTIER <yann.gautier@st.com>