ARM: dts: stm32mp: Add OP-TEE reserved memory to SPL dtb

Add the "/reserved-memory/optee" node to the SPL devicetree. The
purpose is to allow configuring TZC regions when booting OP-TEE.
Signed-off-by: NAlexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>

arch/arm/dts/stm32mp157a-dk1-u-boot.dtsi

@@ -29,9 +29,12 @@
 	};
 
 	reserved-memory {
+		u-boot,dm-spl;
+
 		optee@de000000 {
 			reg = <0xde000000 0x02000000>;
 			no-map;
+			u-boot,dm-spl;
 		};
 	};