ASoC: SOF: ipc4-loader: Verify ext manifest magic number

Firmware image must start with an extended manifest. Add a check to make
sure that the image does contain it.

The magic number (the first u32 of a firmware image if manifest is present)
for an IPC4 image must be 0x31454124 (ASCI "$AE1").

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20220823124219.927-1-peter.ujfalusi@linux.intel.com


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