ASoC: Intel: avs: Use str_on_off() in avs_dsp_core_power()

Remove hard-coded strings by using the str_on_off() helper function.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Link: https://patch.msgid.link/20250212091227.1217-3-thorsten.blum@linux.dev


Reviewed-by: Cezary Rojewski <cezary.rojewski@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>