ASoC: SOF: ext_manifest: parse cavs extra config data elem

ASoC: SOF: ext_manifest: parse cavs extra config data elem

OUTBOX_SIZE, INBOX_SIZE are defined but not being used yet. Handle
these elements to avoid warning about unknown token type.

Signed-off-by: Fred Oh <fred.oh@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Link: https://lore.kernel.org/r/20201127164022.2498406-4-kai.vehmanen@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>