AP_Mission: Support MAV_CMD_DO_FENCE_ENABLE as a mission item.
Plane: Support MAV_CMD_DO_FENCE_ENABLE as a mission item.
Plane: fixed missing break statement
AP_Math: fixed example build
Plane: prepare for 3.2.0 release
plane: Basic Zynq Linux platform support

Preliminary support for Zynq/Linux on the 'ZyboPilot' HW platform.

see https://github.com/trjw/ZyboPilot-bsp for the PetaLinux / Vivado project
files.

At this stage CPPM/Pulse in and PWM out work, and in CLI mode the passthru
test works correctly.

The platform has passed minimal smoke testing in HIL mode.

ZYNQ IS NOT FLIGHT TESTED YET!  FLY THIS PLATFORM AT YOUR OWN RISK!

Signed-off-by: John Williams <john@whelanwilliams.net>
AP_HAL_Linux: Add support for in-kernel SPI CS handling

Add support for /dev/spidev<bus>.<cs> in-kernel SPI CS handling, and convert
existing SPI devices over.

 * Add a new member _subdev to the LinuxSPIDeviceDriver class, and initialiser
   in LinuxSPIDevice constructor.  Use subdev 0 for GPIO-managed CS
 * Extend the _cs_pin to signed 16 bits and define SPI_CS_KERNEL (-1) for
   kernel-managed CS
 * Move to per-device file descriptors (required for in-kernel CS)
 * Extend spidev filenames to include bus and subdevice numbers, possibly
   longer than 1 digit each
 * Allow support for platforms enumerating /dev/spidevNNN from non-zero bases
 * Convert existing users over to the new API

Signed-off-by: John Williams <john@whelanwilliams.net>
AP_HAL_Linux: Bypass manual CS arrerstion for SPI_CS_KERNEL mode

Missed from initial patch series

Signed-off-by: John Williams <john@whelanwilliams.net>
AP_HAL_Linux: Enable SPI-connected MPU9250, MS5611 for Zynq platform

Signed-off-by: John Williams <john@whelanwilliams.net>
AP_Compass: Move HMC5xx3 constants to shared header

Preparing for addition of HMC5983 driver which uses the same register/cmd set

Signed-off-by: John Williams <john@whelanwilliams.net>
AP_Compass: Add support for HMC5983 (SPI mode only)

This is based on the 5843.  Only SPI mode is currently supported

Signed-off-by: John Williams <john@whelanwilliams.net>
Platforms: Enable HMC5983 for Zynq

Signed-off-by: John Williams <john@whelanwilliams.net>