ASoC: SOF: Make sof_ipc_ext_data enum more rigid

It's a part of ABI interface, so enum value shouldn't change
for example after removing some old enum code.

Signed-off-by: Karol Trzcinski <karolx.trzcinski@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200312200622.24477-3-pierre-louis.bossart@linux.intel.com


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