drm/i915/perf: disable clk ratio reports on gen9

We're doing this on all Gen9 based platforms, let's just check the gen
rather than listing every single platforms.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170918112124.29541-2-lionel.g.landwerlin@intel.com