firmware: cs_dsp: Add mock bin file generator for KUnit testing

Add a mock firmware file that emulates what the firmware build tools
would normally create. This will be used by KUnit tests to generate a
test bin file.

The data payload in a bin is an opaque blob, so the mock bin only needs
to generate the appropriate file header and description block for each
payload blob.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://patch.msgid.link/20241212143725.1381013-5-rf@opensource.cirrus.com


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