i915: update to GuC 70.8.0 and HuC 8.5.1 for MTL

Due to changes in the HuC auth flow via GuC, both binaries need to be
updated at the same time to keep compatibility.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>

WHENCE

@@ -4713,10 +4713,10 @@ File: i915/mtl_dmc.bin
 Version: DMC API/APB ver 2 release 12 for Meteorlake
 
 File: i915/mtl_guc_70.bin
-Version: GuC API/APB ver 70.6.6 for Meteorlake
+Version: GuC API/APB ver 70.8.0 for Meteorlake
 
 File: i915/mtl_huc_gsc.bin
-Version: HuC API/APB ver 8.5.0 for Meteorlake
+Version: HuC API/APB ver 8.5.1 for Meteorlake
 
 License: Redistributable. See LICENSE.i915 for details
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