manifest: sof: update to commit e7cb489d4

This updates SOF modules to commit
e7cb489d430dc2181e4a5f7f953ed1eaeec6668d. This includes
a change where rimage is pulled into the tree and is no
longer a submodule. So update the rimage config path so
signing still works.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>