dts: ARM: stm32mp15: add OP-TEE node in u-boot DTSI

Add OP-TEE firmware node in stm32mp15 U-Boot DTSI. This node is
needed since commit [1] that changed U-Boot/stm32mp15 to detect
OP-TEE availability by probing the resource instead of relying on
U-Boot configuration. The software sequence implemented by [1] is
fine but U-Boot DTS/DTSI files were not updated accordingly since,
hence OP-TEE presence is never detected by U-Boot, preventing Linux
kernel from using OP-TEE resources.

For consistency and to synchronize stm32mp15 DTSI files (excluding
U-Boot specific DTSI files) with the Linux kernel ones, this change
also moves the OP-TEE reserved memory nodes from board generic DTSI
files to U-Boot specific board DTSI files.

Link: [1] commit 43df0a15 ("stm32mp1: dynamically detect op-tee presence")
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>