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/package/rpi-rf-mod/Config.in

@@ -0,0 +1,31 @@
+config BR2_PACKAGE_RPI_RF_MOD
+  select BR2_PACKAGE_EQ3_CHAR_LOOP
+  select BR2_PACKAGE_GENERIC_RAW_UART
+  bool "Support for RPI-RF-MOD/HM-MOD-RPI-PCB GPIO HAT"
+
+if BR2_PACKAGE_RPI_RF_MOD
+
+config BR2_PACKAGE_RPI_RF_MOD_DTS
+  bool "Compile Device Tree Overlay"
+
+if BR2_PACKAGE_RPI_RF_MOD_DTS
+
+choice
+  prompt "For Target"
+  default BR2_PACKAGE_RPI_RF_MOD_DTS_RPI
+
+config BR2_PACKAGE_RPI_RF_MOD_DTS_RPI
+  bool "RaspberryPi"
+  help
+    For the RaspberryPi
+
+config BR2_PACKAGE_RPI_RF_MOD_DTS_TINKER
+  bool "ASUS Tinkerboard"
+  help
+    For the ASUS Tinkerboard
+
+endchoice
+
+endif
+
+endif