applications: nrf_desktop: Add boot_partition label to B0 slot in DTS

Add boot_partition as an additional label on b0_partition in the
B0 memory map for nrf52840dk_nrf52840 and nrf5340dk_nrf5340_cpuapp.

Signed-off-by: Marcin Jelinski <marcin.jelinski@nordicsemi.no>

Author: maje-emb

applications/nrf_desktop/configuration/nrf52840dk_nrf52840/memory_map_b0.dtsi

@@ -12,7 +12,8 @@
 		#size-cells = <1>;
 		ranges;
 
-		b0_partition: partition@0 {
+		/* 'boot_partition' is an additional label for the B0 bootloader region. */
+		boot_partition: b0_partition: partition@0 {
 			compatible = "zephyr,mapped-partition";
 			label = "b0";
 			reg = <0x0 DT_SIZE_K(20)>;

applications/nrf_desktop/configuration/nrf5340dk_nrf5340_cpuapp/memory_map_b0.dtsi

@@ -12,7 +12,8 @@
 		#size-cells = <1>;
 		ranges;
 
-		b0_partition: partition@0 {
+		/* 'boot_partition' is an additional label for the B0 bootloader region. */
+		boot_partition: b0_partition: partition@0 {
 			compatible = "zephyr,mapped-partition";
 			label = "b0";
 			reg = <0x0 DT_SIZE_K(32)>;