image_types_fsl.bbclass: typo fix (s/Unkown/Unknown/)

Signed-off-by: Mario Domenech Goulart <mario@ossystems.com.br>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
linux-fslc: Update to 3.17 release

This updates to the 3.17 release. No changes are applied on the
patches-3.17 branch at this moment so it is essentially the hash of
the v3.17 tag.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>