iio: hmc5843: Move hmc5843 out of staging

This patch moves hmc5843 driver from staging/iio/magnetometer
to iio/magnetometer, updates the corresponding Makefiles and
moves the hmc5843* entries to the 'Industrial I/O support ->
Magnetometer sensors' menu.

Signed-off-by: Cristina Moraru <cristina.moraru09@gmail.com>
Cc: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>