drm/i915/bdw: HW context support

BDW context sizes varies a bit.

v2: Squash in fixup for the hw context size from Ben.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net> (v1)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index cc619c1..72a3df3 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -117,6 +117,9 @@
 		else
 			ret = GEN7_CXT_TOTAL_SIZE(reg) * 64;
 		break;
+	case 8:
+		ret = GEN8_CXT_TOTAL_SIZE;
+		break;
 	default:
 		BUG();
 	}