stm32mp1: configs: imply CONFIG_OF_LIBFDT_OVERLAY

Add imply for FDT overlay that can be usefuill for kernel device tree
management but it is not mandatory (can be removed to gain space)

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index cbb2a2a..37b2585 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1567,6 +1567,7 @@
 	imply SPL_SYSRESET
 	imply CMD_DM
 	imply CMD_POWEROFF
+	imply OF_LIBFDT_OVERLAY
 	imply ENV_VARS_UBOOT_RUNTIME_CONFIG
 	imply USE_PREBOOT
 	help