chore: Improve consistency between Blues boards

[zfields]

Builds on work provided by @maxgerhardt, to improve the consistency across Blues boards.

[zfields]

I do have one question.

Is the following:

    "framework_extra_flags": {
      "arduino": "-DCUSTOM_PERIPHERAL_PINS -DPIO_FRAMEWORK_ARDUINO_ENABLE_CDC"
    },

used to provide a default, or will that make it ALWAYS true?

I am specifically interested in -DPIO_FRAMEWORK_ARDUINO_ENABLE_CDC. If it cannot be disabled, then I went the wrong direction, and I would need to remove it from Cygnet as well.

[valeros]

I am specifically interested in -DPIO_FRAMEWORK_ARDUINO_ENABLE_CDC. If it cannot be disabled, then I went the wrong direction, and I would need to remove it from Cygnet as well.

This flag will be always added, unless it's disabled via the build_unflags option.

Please also move -DARDUINO_CYGNET and -DARDUINO_SWAN_R5 to framework_extra_flags field.