Can you explain why I would need the `dtoverlay=` line?The original UDRC & some of the UDRC II HATs have their DT (Device Tree)
overlay files in EEPROM on the HAT. The DT overlay in the HAT EEPROM is
automatically loaded by the boot firmware. The DT overlay file for the
UDRC II & DRAWS HATs grew too large for the EEPROM so are now only
loaded dynamically from the /boot/overlays directory.
Using dtoverlay= ends the current overlay scope so that the UDRC or
DRAWS overlay in the /boot/overlays directory can be loaded by a
subsequent dtoverlay=udrc or dtoverlay=draws command.
dtoverlay= effectively suppresses the loading of the HAT overlay in EEPROM.
Any dtparam or dtoverlay directives must come after the dtoverlay= line.