Serial number handling

[martinling]

This PR updates EUT serial number handling during the test.

• The Black Magic Probe is used to read out the MCU serial number over SWD, as part of the same GDB script that is used to flash Saturn-V.
  • This gives us the earliest possible opportunity to associate a unique EUT with a given test result, which will work even in the event of a fault preventing USB enumeration.
• The serial number as read by the BMP is translated to the Base32 format used by Saturn-V.
• Apollo is updated to use the same Base32 format, by merging in firmware: Use Base32 for the serial number in SAMD11/SAMD21 boards apollo#37.
• The find_device helper is extended to check that USB descriptors for the MCU match the expected Base32 string.
• Adds readout of configuration flash UID, using Add a method to read the 64-bit UID of the configuration flash chip apollo#40.