[nrf fromtree] boards: Add secondary_app_partition alias

Add secondary_app_partition aliases.
Those aliases can be used to configure the code partition for the
second copy of the FW in the Direct XIP update scenarios.

Signed-off-by: Tomasz Chyrowicz <[email protected]>
(cherry picked from commit e3c5bdf)

Author: tomchy

boards/nordic/nrf54h20dk/nrf54h20dk_nrf54h20_cpuapp.dts

@@ -18,7 +18,7 @@
 
 	chosen {
 		zephyr,console = &uart136;
-		zephyr,code-partition = &slot0_partition;
+		zephyr,code-partition = &cpuapp_slot0_partition;
 		zephyr,flash = &mram1x;
 		zephyr,sram = &cpuapp_data;
 		zephyr,shell-uart = &uart136;
@@ -193,6 +193,8 @@ slot0_partition: &cpuapp_slot0_partition {
 	label = "image-0";
 };
 
+secondary_app_partition: &cpuapp_slot1_partition {};
+
 slot1_partition: &cpuapp_slot1_partition {
 	label = "image-1";
 };

boards/nordic/nrf54h20dk/nrf54h20dk_nrf54h20_cpurad.dts

@@ -90,6 +90,8 @@ slot0_partition: &cpurad_slot0_partition {
 	label = "image-0";
 };
 
+secondary_app_partition: &cpurad_slot1_partition {};
+
 slot1_partition: &cpurad_slot1_partition {
 	label = "image-1";
 };