Linux: Add support for SPIDEV (#734)

RPi and Linux refactor.

Add GPIO Sysfs for GPIO operations.

Update configure script.

Fix some cppcheck warnings.

Add serial emulation that prints to stdout.

Fix some file headers.

MySensors.h

@@ -66,12 +66,8 @@
 #elif defined(ARDUINO_ARCH_SAMD)
 #include "core/MyHwSAMD.cpp"
 #elif defined(__linux__)
-#ifdef LINUX_ARCH_RASPBERRYPI
-#include "core/MyHwRPi.cpp"
-#else
 #include "core/MyHwLinuxGeneric.cpp"
 #endif
-#endif
 
 // LEDS
 #if !defined(MY_DEFAULT_ERR_LED_PIN) && defined(MY_HW_ERR_LED_PIN)
@@ -254,7 +250,7 @@ MY_DEFAULT_RX_LED_PIN in your sketch instead to enable LEDs
 #include "drivers/AVR/DigitalIO/DigitalIO.h"
 #endif
 
-#if defined(MY_RADIO_NRF24) && defined(__linux__) && !defined(LINUX_ARCH_RASPBERRYPI)
+#if defined(MY_RADIO_NRF24) && defined(__linux__) && !(defined(LINUX_SPI_BCM) || defined(LINUX_SPI_SPIDEV))
 #error No support for nRF24 radio on this platform
 #endif