snippets: sdp: mspi: add software-multiperipheral

Since switching between peripheral devices is done in SW,
add appropriate binding.

Signed-off-by: Marcin Szymczyk <marcin.szymczyk@nordicsemi.no>

Author: masz-nordic

snippets/sdp/mspi/sdp-mspi-app.overlay

@@ -9,6 +9,7 @@
 
 	sdp_mspi: sdp_mspi {
 		compatible = "nordic,nrfe-mspi-controller";
+		software-multiperipheral;
 		#address-cells = <1>;
 		#size-cells = <0>;
 	};