Support for RPI-RF-MOD/HM-MOD-RPI-PCB for HomeMatic/homematicIP communication (#1266)

* add eq3_char_loop package (eQ-3 char loopback kernel module)

* add generic_raw_uart package (low-latency raw UART kernel driver)

* add rpi-rf-mod package 

* add device tree overlay support for RPI-RF-MOD/HM-MOD-RPI-PCB on Raspberry Pi

* enable GPIOLIB and GPIO_SYSFS required for RPI-RF-MOD/HM-MOD-RPI-PCB support.

* add basic RPI-RF-MOD/HM-MOD-RPI-PCB support for ASUS Tinker Board

* add device tree overlay support for ASUS Tinker Board and add
haos-config.txt loading support to U-Boot boot script

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

@@ -10,6 +10,7 @@ function hassos_pre_image() {
     cp "${BINARIES_DIR}"/*.dtb "${BOOT_DATA}/"
     cp -r "${BINARIES_DIR}/rpi-firmware/"* "${BOOT_DATA}/"
     cp "${BOARD_DIR}/../boot-env.txt" "${BOOT_DATA}/config.txt"
+    cp "${BINARIES_DIR}"/*.dtbo "${BOOT_DATA}/overlays/"
 
     # EEPROM update for Raspberry Pi 4/Compute Module 4
     if grep -Eq "^BR2_PACKAGE_RPI_EEPROM=y$" "${BR2_CONFIG}"; then