This updates the minimal supported version of CMake to 3.16, which in turn enables us to use more CMake features and have a cleaner build system.
This is the version that provides most new features and also the one we use in our latest docker image for CI.
The legacy driver can't handle the breaking change between esp chips
very well.
And it's not elegant to extend new feature like DMA, ETM.
The new driver can return a opaque handle for each RMT channel.
An obvious transaction concept was also introduced.
TX and RX functionalities are splited out.
