Misc fixes

Here is a handle of small miscellaneous fixess, three of them based on things from the OP crew

- fix mode for ground/gcs/bin/gcs to suppress warning during make package on linux (Oleg)
- support for coax octo in vtol follower (Sambas)
- change malloc to the freertos implementation (forgot)
- make sure systemmod cpuload is never negative (me)
- weird typo in stabilization, no affect but bad code (me)