Sensor drivers

These are sensor driver improvements / new laser rangefinder kindly contributed by the APM dev community.
These check out. It means that the GPIOs get configured twice during board boot up right now, but this should do no harm.

What is more worrisome is that this dual use can result in the pin config pulled low on another bus during the transfer on that bus on FMUv2 if the SPI4 devices are contacted. This condition is ok if we ever only probe the external bus at startup and not during runtime and/or alternatively mutually lock out the FMUv2 sensor SPI and the FMUv3 external SPI when using these pins.