Read in GPIO 5-bit Device Serial Number

[dniklaus]

Description Read 5 bit Device Serial Number, use Feather M0 MCU's GPIO as follows:

• Bit 0: Pin A0 (14)
• Bit 1: Pin A1 (15)
• Bit 2: Pin A2 (16)
• Bit 3: Pin A3 (17)
• Bit 4: Pin A4 (18)

Acceptance Criteria

• let the 5 GPIO pins operate as inputs with pullup (=> use pinMode(A0, INPUT_PULLUP), as described in the Adafruit Feather M0 manual), open pins will the read in as HIGH
• reading in the GPIO bits at startup
• minimal module integration test shows the correct function of the feature

Tasks

• [x] #38
• [x] #39
• [x] #40
• [x] #41
• [x] #42