- increase stack sizes to run cleanly under stackcheck
- this is likely overkill for most boards, but using stackcheck to set our minimum ensures we have a very safe margin on regular builds and it's something we can currently afford
- remove holybro_durandal-v1_stackcheck from test rack (there's only one unit)
- this doesn't currently change anything, but gets us ready to start
experimenting with using the small amount of instruction tightly memory
on STM32F7
- the .ramfuncs section works with NuttX CONFIG_ARCH_RAMFUNCS
- update to NuttX with stm32f4 and stm32f7 SPI DMA internal buffers
- remove explicit DMA buffer allocations from new IMU drivers
- restore original BOARD_DMA_ALLOC_POOL_SIZE
- decrease SPI DMA thresholds based on fmu-v2/v3/v4/v5 bench testing
