ASoC: SOF: debug: Handle cases when fw_lib_prefix is not set, NULL

The firmware libraries are not supported by IPC3, the fw_lib_path is not
a valid parameter and it is always NULL.
Do not create the debugfs file for IPC3 at all as it is not applicable.

With IPC4 some vendors/platforms might not support loadable libraries and
the fw_lib_prefix is left to NULL to indicate this.
Handle such case with allocating "Not supported" string.

Reviewed-by: Marc Herbert <marc.herbert@intel.com>
Fixes: 17f40412 ("ASoC: SOF: debug: show firmware/topology prefix/names")
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20240426153902.39560-2-pierre-louis.bossart@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>