Relocate the machine handling functions from sof-audio.c to core.c to
maintain code separation.

While doing the move, drop the redundant
IS_ERR_OR_NULL(plat_data->pdev_mach) check from
sof_machine_unregister()
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Link: https://lore.kernel.org/r/20231129125327.23708-3-peter.ujfalusi@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>