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 <Torsten.Rasmussen@nordicsemi.no>
Torsten Rasmussen