drm/i915: Add HAS_CORE_RING_FREQ macro

Added a new HAS_CORE_RING_FREQ macro, currently used in
gen6_update_ring_freq & i915_ring_freq_table debugfs function.
The programming & read of ring frequency table is needed for newer
GEN(>=6) platforms, except VLV/CHV.

Issue: VIZ-5144
Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Akash Goel <akash.goel@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1784,7 +1784,7 @@ static int i915_ring_freq_table(struct seq_file *m, void *unused)
 	int gpu_freq, ia_freq;
 	unsigned int max_gpu_freq, min_gpu_freq;
 
-	if (!(IS_GEN6(dev) || IS_GEN7(dev))) {
+	if (!HAS_CORE_RING_FREQ(dev)) {
 		seq_puts(m, "unsupported on this chipset\n");
 		return 0;
 	}