.. however, the number of endpoints is only set for SAMD (8).
Other ports need to set the value. Otherwise, the build will show
the message
```
Unable to check whether maximum number of endpoints is respected
```
In cases where more than one board is connected to a single computer it can become pretty hard to figure out which board you're actually talking to. For example, if you have several MIDI-compatible boards they all show up as "CircuitPython MIDI". This change allows boards to replace the "CircuitPython" part of their USB descriptors with more specific text, for example, "CircuitPython Feather" or just "Feather". This will let folks more easily tell boards apart.
The new option is named `USB_INTERFACE_NAME` and is available in `mkconfigboard.mk`. For example:
```
USB_INTERFACE_NAME = "Feather"
```
This started while adding USB MIDI support (and descriptor support is
in this change.) When seeing that I'd have to implement the MIDI class
logic twice, once for atmel-samd and once for nrf, I decided to refactor
the USB stack so its shared across ports. This has led to a number of
changes that remove items from the ports folder and move them into
supervisor.
Furthermore, we had external SPI flash support for nrf pending so I
factored out the connection between the usb stack and the flash API as
well. This PR also includes the QSPI support for nRF.
