HAL_PX4: enable right FMUv2 drivers

ets_airspeed is ok, but mkblctrl driver doesn't build yet
PX4: added px4-v2 targets
PX4: added io-v2 targets
PX4: moved px4io-*.bin to ROMFS

this is more convenient than users having to copy it over
PX4: adapt rc.APM for FMUv1 and FMUv2
HAL_PX4: some GPIO functions are not available on FMUv2 yet
PX4: disable bma180 driver for FMUv1
HAL_PX4: fixed build on FMUv1
PX4: enable airspeed base driver and meas driver

this uses the new airspeed parent driver from Lorenz
AP_Math: added a quick test of floating point location accuracy

just confirming some maths ...
PX4: fixed airspeed build on FMUv1
AP_HAL: added RCOutput example sketch

useful for testing all 14 channels via APM API
HAL_PX4: fixed GPIO build

don't use vehicle includes
PX4: disable mixer load for now

loading a mixer disables IO output
PX4: expand pass thru mixer to 8 channels

we're not using it now, but when we do use it we want all 8 channels
PX4: fixed build of v1 and v2 firmwares in one build

this does a clean on each build, which is horribly inefficient. To fix
that we need to work out what state information is preventing
switching targets in one build
PX4: only put one IO firmware in ROMFS

saves a bit of space. This also fixes makefile based upload
PX4: Changed the startup script to have mavlink on USART2 / Serial 1 on FMUv2
HAL_PX4: support up to 16 analog channels
PX4: allow NuttX tree to be in directory above Firmware tree