Add rpi-eeprom firmware (#939)

* Add 2020-10-28 beta EEPROM

This improves boot from USB and speeds up boot times.
also includes sd card v1 boot reliability.
see https://github.com/raspberrypi/rpi-eeprom/pull/246

Also add HDMI_DELAY=0 so HDMI display is always visible
for easier debugging.

buildroot-external/board/raspberrypi/hassos-hook.sh

@@ -15,6 +15,8 @@ function hassos_pre_image() {
     if [[ "${BOARD_ID}" =~ "rpi4" ]]; then
         cp "${BINARIES_DIR}/rpi-firmware/fixup.dat" "${BOOT_DATA}/fixup4.dat" 
         cp "${BINARIES_DIR}/rpi-firmware/start.elf" "${BOOT_DATA}/start4.elf" 
+        cp "${BINARIES_DIR}/rpi-eeprom/pieeprom.sig" "${BOOT_DATA}/pieeprom.sig"
+        cp "${BINARIES_DIR}/rpi-eeprom/pieeprom.upd" "${BOOT_DATA}/pieeprom.upd"
     else
         cp -t "${BOOT_DATA}" \
             "${BINARIES_DIR}/rpi-firmware/fixup.dat" \