This creates a common safe mode mechanic that ports can share.
As a result, the nRF52 now has safe mode support as well.
The common safe mode adds a 700ms delay at startup where a reset
during that window will cause a reset into safe mode. This window
is designated by a yellow status pixel and flashing the single led
three times.
A couple NeoPixel fixes are included for the nRF52 as well.
Fixes#1034. Fixes#990. Fixes#615.
We were writing with quad page program including the address (0x38)
which is unsupported by the GD25Q16C but it is supported by the
flash on the DK. So, we use the single address, quad data command
(0x32).
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.
