RC input and PWM output for Navio2

cmake/configs/posix_rpi2_release.cmake

posix-configs/rpi2/mainapp.config

src/drivers/pwm_out/CMakeLists.txt

src/drivers/pwm_out/pwm_out.cpp

src/modules/commander/PreflightCheck.cpp

src/modules/mavlink/mavlink_main.cpp

src/modules/rcinput/CMakeLists.txt

src/modules/rcinput/rcinput.cpp

src/platforms/posix/px4_layer/px4_posix_tasks.cpp