imx8m: Guard binman nodes with CONFIG_OPTEE

Guard binman nodes with CONFIG_OPTEE to fix the following error
when building without optee support:

  BINMAN  .binman_stamp
Image 'image' has faked external blobs and is non-functional: tee.bin

Image 'image' is missing optional external blobs but is still functional: tee-os

/binman/section/fit/images/tee/tee-os (tee.bin):
   See the documentation for your board. You may need to build Open Portable
   Trusted Execution Environment (OP-TEE) and build with TEE=/path/to/tee.bin

Some images are invalid
make: *** [Makefile:1135: .binman_stamp] Error 103

While at it, only pass tee to the loadables lines when CONFIG_OPTEE is
defined.

Reported-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Tested-by: Yannic Moog <y.moog@phytec.de>
diff --git a/arch/arm/dts/imx8mn-u-boot.dtsi b/arch/arm/dts/imx8mn-u-boot.dtsi
index 4a4498b..bf2bb0f 100644
--- a/arch/arm/dts/imx8mn-u-boot.dtsi
+++ b/arch/arm/dts/imx8mn-u-boot.dtsi
@@ -240,6 +240,7 @@
 					};
 #endif
 
+#ifdef CONFIG_OPTEE
 					tee: tee {
 						description = "OP-TEE";
 						type = "tee";
@@ -254,6 +255,7 @@
 							optional;
 						};
 					};
+#endif
 
 					binman_fip: fip {
 						arch = "arm64";
@@ -283,7 +285,11 @@
 						fdt = "fdt-SEQ";
 						firmware = "uboot";
 #ifndef CONFIG_ARMV8_PSCI
+#ifdef CONFIG_OPTEE
 						loadables = "atf", "tee";
+#else
+						loadables = "atf";
+#endif
 #endif
 					};
 				};