drm/i915: Add ddb size field to device info structure

Adding the ddb size into the devide info will avoid
platform checks while computing wm.

v2: Added comment and WARN_ON if ddb size is zero.(Jani)
v3: Added WARN_ON at the right place.(Jani)

Suggested-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Deepak M <m.deepak@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1473931870-7724-1-git-send-email-m.deepak@intel.com

drivers/gpu/drm/i915/i915_pci.c

@@ -328,6 +328,7 @@ static const struct intel_device_info intel_skylake_info = {
 	.gen = 9,
 	.has_csr = 1,
 	.has_guc = 1,
+	.ddb_size = 896,
 };
 
 static const struct intel_device_info intel_skylake_gt3_info = {
@@ -336,6 +337,7 @@ static const struct intel_device_info intel_skylake_gt3_info = {
 	.gen = 9,
 	.has_csr = 1,
 	.has_guc = 1,
+	.ddb_size = 896,
 	.ring_mask = RENDER_RING | BSD_RING | BLT_RING | VEBOX_RING | BSD2_RING,
 };
 
@@ -358,6 +360,7 @@ static const struct intel_device_info intel_broxton_info = {
 	.has_hw_contexts = 1,
 	.has_logical_ring_contexts = 1,
 	.has_guc = 1,
+	.ddb_size = 512,
 	GEN_DEFAULT_PIPEOFFSETS,
 	IVB_CURSOR_OFFSETS,
 	BDW_COLORS,
@@ -369,6 +372,7 @@ static const struct intel_device_info intel_kabylake_info = {
 	.gen = 9,
 	.has_csr = 1,
 	.has_guc = 1,
+	.ddb_size = 896,
 };
 
 static const struct intel_device_info intel_kabylake_gt3_info = {
@@ -377,6 +381,7 @@ static const struct intel_device_info intel_kabylake_gt3_info = {
 	.gen = 9,
 	.has_csr = 1,
 	.has_guc = 1,
+	.ddb_size = 896,
 	.ring_mask = RENDER_RING | BSD_RING | BLT_RING | VEBOX_RING | BSD2_RING,
 };