zephyr: fix handling of devicetree overlays in mcuboot

The current specific setting of devicetree overlay files using `set()`
has a couple of built-in flaws.

It keeps readding the overlay file on each subsequent CMake invocation.
The build command (make/ninja), will automatically invoke CMake if there
are any changes to files used as configure time dependencies.

This can easily be seen by manually re-invoking CMake:
```
 # First invocation
$ cmake -DBOARD=nrf52840dk_nrf52840  -DDTC_OVERLAY_FILE=custom.dts ..
Loading Zephyr default modules (Zephyr workspace).
-- Application: /projects/github/ncs/bootloader/mcuboot/boot/zephyr
...
-- Found devicetree overlay: custom.dts
-- Found devicetree overlay: bootloader/mcuboot/boot/zephyr/dts.overlay

 # Second invocation
$ cmake -DBOARD=nrf52840dk_nrf52840  -DDTC_OVERLAY_FILE=custom.dts ..
Loading Zephyr default modules (Zephyr workspace).
-- Application: /projects/github/ncs/bootloader/mcuboot/boot/zephyr
...
-- Found devicetree overlay: custom.dts
-- Found devicetree overlay: mcuboot/boot/zephyr/dts.overlay
-- Found devicetree overlay: mcuboot/boot/zephyr/dts.overlay
```

Zephyr has built-in support for application specific overlay config
which gets automatically applied when the overlay file is named:
`app.overlay`.

Therefore rename `dts.overlay` to `app.overlay`.
Ref: https://docs.zephyrproject.org/3.2.0/build/dts/howtos.html \
  #set-devicetree-overlays

This change further allows users of mcuboot to place their mcuboot
configuration out-of-tree of the sample by using the
`APPLICATION_CONFIG_DIR` setting.

Signed-off-by: Torsten Rasmussen <[email protected]>

Author: tejlmand

boot/zephyr/CMakeLists.txt

@@ -6,19 +6,6 @@
 
 cmake_minimum_required(VERSION 3.13.1)
 
-# Add a common dts overlay necessary to ensure mcuboot is linked into,
-# and fits inside, the boot partition. (If the user specified a
-# DTC_OVERLAY_FILE on the CMake command line, we need to append onto
-# the list).
-if(DTC_OVERLAY_FILE)
-  set(DTC_OVERLAY_FILE
-    "${DTC_OVERLAY_FILE} ${CMAKE_CURRENT_LIST_DIR}/dts.overlay"
-    CACHE STRING "" FORCE
-    )
-else()
-  set(DTC_OVERLAY_FILE ${CMAKE_CURRENT_LIST_DIR}/dts.overlay)
-endif()
-
 # Enable Zephyr runner options which request mass erase if so
 # configured.
 #

boot/zephyr/dts.overlay renamed to boot/zephyr/app.overlay

@@ -19,32 +19,32 @@ tests:
   sample.bootloader.mcuboot.usb_cdc_acm_recovery:
     tags: bootloader_mcuboot
     platform_allow:  nrf52840dongle_nrf52840
-    extra_args: DTC_OVERLAY_FILE=./usb_cdc_acm.overlay
+    extra_args: DTC_OVERLAY_FILE="./usb_cdc_acm.overlay;app.overlay"
     integration_platforms:
       - nrf52840dongle_nrf52840
   sample.bootloader.mcuboot.usb_cdc_acm_recovery_log:
     extra_args: OVERLAY_CONFIG=./usb_cdc_acm_log_recovery.conf
-      DTC_OVERLAY_FILE=./boards/nrf52840_big.overlay
+      DTC_OVERLAY_FILE="./boards/nrf52840_big.overlay;app.overlay"
     platform_allow:  nrf52840dk_nrf52840
     integration_platforms:
       - nrf52840dk_nrf52840
     tags: bootloader_mcuboot
   sample.bootloader.mcuboot.single_slot:
     extra_args: OVERLAY_CONFIG=./single_slot.conf
-      DTC_OVERLAY_FILE=./boards/nrf52840_single_slot.overlay
+      DTC_OVERLAY_FILE="./boards/nrf52840_single_slot.overlay;app.overlay"
     platform_allow:  nrf52840dk_nrf52840
     integration_platforms:
       - nrf52840dk_nrf52840
     tags: bootloader_mcuboot
   sample.bootloader.mcuboot.qspi_nor_slot:
-    extra_args: DTC_OVERLAY_FILE=./boards/nrf52840dk_qspi_nor_secondary.overlay
+    extra_args: DTC_OVERLAY_FILE="./boards/nrf52840dk_qspi_nor_secondary.overlay;app.overlay"
       OVERLAY_CONFIG="./boards/nrf52840dk_qspi_nor.conf;./boards/nrf52840dk_qspi_secondary_boot.conf"
     platform_allow: nrf52840dk_nrf52840
     integration_platforms:
       - nrf52840dk_nrf52840
     tags: bootloader_mcuboot
   sample.bootloader.mcuboot.hooks_multi:
-    extra_args: DTC_OVERLAY_FILE=./boards/nrf52840dk_ram_multi.overlay
+    extra_args: DTC_OVERLAY_FILE="./boards/nrf52840dk_ram_multi.overlay;app.overlay"
       OVERLAY_CONFIG=./boards/nrf52840dk_hooks_sample_overlay.conf
       TEST_BOOT_IMAGE_ACCESS_HOOKS=Y
     platform_allow: nrf52840dk_nrf52840