This is a step towards isolating time from the system.

Fixes these invalid format strings:
- A `%d` for a pointer (replaced it by `%p`)
- A 0x%08x (and a 0x%0x8!) for a pointer (replaced by %p)
- 2 cases of `%d` for a `ssize_t` (replaced it by `%zi`)
- 1 case of a %u for an `int` (replaced by %i)
- 3 cases of %d for a `long` (replaced by %ld)
- 19 cases of `%d`, `%i`, `%u` or `%lu` for a `size_t` (replaced it by `%zu`)
- An unused formatting argument (removed it)
- A missing `%d` (added it)
- A missing `%s` (added it)
- 2 cases of `%llu` for a `uint64_t` (replaced it by `"%" PRIu64`)
- 6 cases of giving a string directly as format string (replaced it by `("%s", string)`)
- 2 cases of %*-s, which should probably have been %-*s.
  (Looks like NuttX accepts (the invalid) %*-s, but other platforms don't.)
- A %04x for a `uint32_t` (replaced by "%04" PRIx32)

 - px4_add_module now requires MAIN
 - px4_add_library doesn't automatically link

The learned ekf2 mag bias values are invalidated when the sensor calibration is updated and must be reset.

The reason for this change is that RPi2 and RPi3 are compatible, and
hopefully all differences coming up can be resolved without ifdefs but
at runtime.

The device ID is defined as a uint32_t in the driver and topic but
stored as a int32_t param. It is therefore sufficient if the device ID
is not 0 in order to be valid.