drm/i915: Organize bind_vma funcs

Let's be optimistic that for future platforms this will remain the same
and reorg a bit.
This reorg in if blocks instead of switch make life easier for future
platform support addition.

Cc: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -2243,29 +2243,18 @@ static struct i915_vma *__i915_gem_vma_create(struct drm_i915_gem_object *obj,
 	vma->obj = obj;
 	vma->ggtt_view = *view;
 
-	switch (INTEL_INFO(vm->dev)->gen) {
-	case 9:
-	case 8:
-	case 7:
-	case 6:
+	if (INTEL_INFO(vm->dev)->gen >= 6) {
 		if (i915_is_ggtt(vm)) {
 			vma->unbind_vma = ggtt_unbind_vma;
 			vma->bind_vma = ggtt_bind_vma;
 		} else {
 			vma->unbind_vma = ppgtt_unbind_vma;
 			vma->bind_vma = ppgtt_bind_vma;
 		}
-		break;
-	case 5:
-	case 4:
-	case 3:
-	case 2:
+	} else {
 		BUG_ON(!i915_is_ggtt(vm));
 		vma->unbind_vma = i915_ggtt_unbind_vma;
 		vma->bind_vma = i915_ggtt_bind_vma;
-		break;
-	default:
-		BUG();
 	}
 
 	list_add_tail(&vma->vma_link, &obj->vma_list);