drm/i915/cnl: Introduce Cannonlake platform defition.

Cannonlake is a Intel® Processor containing Intel® HD Graphics
following Kabylake.

It is Gen10.

Let's start by adding the platform definition based on previous
platforms but yet as alpha_support.

On following patches we will start adding PCI IDs and the
platform specific changes.

CNL has an increased DDB size as Damien had previously
noticed and provided a separated patch that got squashed here.

v2: Squash DDB size here per Ander request.

Credits-to: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1496781040-20888-1-git-send-email-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/i915_pci.c

@@ -425,6 +425,14 @@ static const struct intel_device_info intel_kabylake_gt3_info = {
 	.ring_mask = RENDER_RING | BSD_RING | BLT_RING | VEBOX_RING | BSD2_RING,
 };
 
+static const struct intel_device_info intel_cannonlake_info = {
+	BDW_FEATURES,
+	.is_alpha_support = 1,
+	.platform = INTEL_CANNONLAKE,
+	.gen = 10,
+	.ddb_size = 1024,
+};
+
 /*
  * Make sure any device matches here are from most specific to most
  * general.  For example, since the Quanta match is based on the subsystem