ASoC: SOF: Introduce offset in firmware data

It makes possible to provide extra information to host
before downloading firmware. Extra data should be put
at the beginning of firmware binary.
Exchange is done without any effort on DSP side.
This mechanism will be used in extended manifest.

Signed-off-by: Karol Trzcinski <karolx.trzcinski@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Link: https://lore.kernel.org/r/20200415202816.934-4-pierre-louis.bossart@linux.intel.com


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