drm/xe/guc: Switch to major-only GuC FW tracking for MTL

drm/xe/guc: Switch to major-only GuC FW tracking for MTL

Newer HuC binaries for MTL (8.5.1+) require GuC 70.7 or newer, so we
need to move on from 70.6.4. Given that the MTL GuC uses major-only
version matching in i915, we can do the same here instead of just
bumping the version (and having to push the versioned binaries,
because they're not there already for i915).

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>