Build all tests of module mcuboot

[nvlsianpu]

only test for frdm_k64f board are build for mcuboot project
I expected that all test for which platform_allow: in https://github.com/zephyrproject-rtos/mcuboot/blob/master/boot/zephyr/sample.yaml of should be tested.
For MCUBoot nrf52840 boards are used as target for integration test (all of them are expected to be build-only)

Neither nrf52840dk_nrf52840 nor nrf52840dongle_nrf52840 are integration platform which cause impossible to use it for mcuboot's integration test.

These a few mcuboot integration tests are testing a few basic configuration build.

[PerMac]

With the #29829 merged this should be possible by adding platforms that need to be tested (build level in case of not simulated ones) in integration_platforms list. This list expands/limits the CI to the platforms in the list (platform_allow only works as an additional filter preventing anything that is not on the list from being tested).

[nvlsianpu]

@PerMac Have to check again, but as i remember mcuboot was not build even with these hints. Maybe because it is external application.

[nordic-krch]

Just wanted to mention that was just fixing an issue with mcuboot failing to compile in certain configuration (reported by downstream project) #35765. It is not verified by zephyr CI though.

[nvlsianpu]

Can building of MCUboot be added to the CI? I think additional twister run with --testcase-root set to bootloader/mcuboot/boot/zephyr will do the job.

@carlescufi Can this be considered and implemented? Maybe this need TSC approval.

Here draft with modified sample.yaml
mcu-tools/mcuboot#890