gen_display_resources: Always treat the sample file as utf-8.
gen_display_resources: Always treat the sample file as utf-8.

This may help resolve the build problems reported at
#4750.

adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython