arm: dts: k3-*-binman: Make default DM file optional

The default DM firmware path is non-optional as of now. Make it
optional so that users that choose to provide DM via TI_DM argument
instead of BINMAN_INDIRS can do so without build errors.

Signed-off-by: Neha Malcom Francis <n-francis@ti.com>
Reviewed-by: Kamlesh Gurudasani <kamlesh@ti.com>
diff --git a/arch/arm/dts/k3-j721e-binman.dtsi b/arch/arm/dts/k3-j721e-binman.dtsi
index 97ee695..bffce03 100644
--- a/arch/arm/dts/k3-j721e-binman.dtsi
+++ b/arch/arm/dts/k3-j721e-binman.dtsi
@@ -307,6 +307,7 @@
 		filename = "ti-dm.bin";
 		blob-ext {
 			filename = "ti-dm/j721e/ipc_echo_testb_mcu1_0_release_strip.xer5f";
+			optional;
 		};
 	};
 	ti-spl {