HAL_Linux: added SBUS decoder from PX4 project

thanks Lorenz!
HAL_Linux: initial support for parallel SBUS and PPM-SUM decoding
Linux_HAL_Essentials: change ring buffer to 300 entries

this ensures full SBUS frames can be decoded
HAL_Linux: change ring buffer to 300 entries
Linux_HAL_Essentials: rebuilt rcinpru0 with 300 ring buffer entries

thanks to Sid for doing this