Add sof-ipc4-v2.8.1/mtl/, intel-signed + community

The intel-signed sof-mtl.ri was shared by Adrian Bonislawski. The
internal build ID is 13643478

Linux test plan ID is 38141.

There has been zero "tools/" changes between v2.8 and v2.8.1; so the
v2.8.x/tools-v2.8/ directory can be re-used as is.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

Author: marc-hb

v2.8.x/sof-ipc4-v2.8.1/mtl/community/sof-mtl.ri

@@ -0,0 +1 @@
+intel-signed/sof-mtl.ri