Support flashing with QMK Toolbox and `qmk` CLI; align licensing with QMK

[davidxia]

"How to Configure your ALT Keyboard" [1] last updated 2018-10-19 states:

We are working with Jack and the other QMK contributors to get the loader application integrated into the next version of QMK Toolbox to simplify this loading process.

It seems flashing with QMK Toolbox and qmk CLI [2] are still unsupported. When I run qmk compile I see the following warning message.

This MCU support package has a lack of support from the upstream provider (Massdrop).
There are currently questions about valid licensing, and at this stage it's likely
their boards and supporting code will be removed from QMK in the near future. Please
contact Massdrop for support, and encourage them to align their future board design
choices to gain proper license compatibility with QMK.

Related Github issues

• Massdrop requirements before next board gets merged qmk/qmk_firmware#11119
• Warn when building a board that uses arm_atsam qmk/qmk_firmware#10904

1: https://drop.com/talk/10343/how-to-configure-your-alt-keyboard
2: https://drop.com/talk/10343/how-to-configure-your-alt-keyboard