Layer detection should not require DFP to fullfil mounted device

[ReinhardKeil]

The Problem To Be Solved

In CMSIS-Toolbox 2.6.1 it was not required to specify the DFP as the mounted device was not checked during layer detection.

cbuild v2.6.1-25-g3f083c7 requires now the DFP, otherwise it reports:

error csolution: board mounted device STM32F756ZGTx not found
error csolution: no compatible software layer found. Review required connections of the project

To duplicate

Use https://github.com/Arm-Examples/AWS_MQTT_Demo and modify Demo.csolution.yml as shown here:

  packs:
    - pack: ARM::[email protected]
    - pack: Keil::[email protected] # Add BSP
#    - pack: Keil::[email protected]
    - pack: ARM::[email protected] # Add CMSIS-Driver for WiFi Shields

  target-types:

    - type: MyBoard
      board: NUCLEO-F756ZG

Related #1889

[brondani]

I thought it was clear since I asked for confirmation. This is a side effect of PR #1875 addressing issues #1841 and #1850.

The expectation is that all required packs (including DFPs) are listed in the solution itself, not in candidate layers.