* CF/BF - Set STM32F7 SPI FAST clock to 13.5Mhz - Gyros not stable at
27mhz.
* CF/BF - Initial SPRacingF7DUAL commit.
Support two simultaneous gyro support (code by Dominic Clifton and Martin Budden)
There are new debug modes so you can see the difference between each gyro.
Notes:
* spi bus instance caching broke spi mpu detection because the detection
tries I2C first which overwrites the selected bus instance when using
dual gyro.
* ALL other dual-gyro boards have one sensor per bus. SPRacingF7DUAL is has two per bus and thus commit has a lot of changes to fix SPI/BUS/GYRO initialisation issues.
* CF/BF - Add SPRacingF4EVODG target.
This target adds a second gyro to the board using the SPI pads on the back of the board.
* CF/BF - Temporarily disable Gyro EXTI pin to allow NEO target to build.
