AP_Math: fixed build of vectorN class on PX4
AP_HAL: added HAL_CPU_CLASS define for selecting algorithms

this will make it easier to select the appropiate level of algorithm
for a CPU
AP_Baro: use HAL_CPU_CLASS in baro driver
DataFlash: use HAL_OS_POSIX_IO
HAL_Linux: fixed build
Plane: default LOG_BITMASK to 32767 on non-APM