CFG_TUSB_OS as cmake parameter

[rapzak]

Hi,

Could you add a cmake parameter to set the CFG_TUSB_OS

This way we can use the SDK's tinyusb lib in freertos programs as well...

see: https://www.eevblog.com/forum/microcontrollers/rp2040-how-to-use-freertos-with-tinyusb/