drm/i915/cfl: Introduce Coffee Lake platform definition.

Coffee Lake is a Intel® Processor containing Intel® HD Graphics
following Kabylake.

It is Gen9 graphics based platform on top of CNP PCH.

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

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

v2: Also add BS2 ring that is present on GT3. As on KBL, according
    spec: "GT3 also has additional media blocks with second instance
    of VEBox and VDBox each", i.e. BSD2 ring in our case. Noticed
    when reviewing PCI ID patches.

v3: CFL_PLATFORM instead for CFL_FEATURES because it contains
    Platform information and no new features when compared to
    BDW_FEATURES definition.

v4: Rebased on top of Cannonlake patches.

Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1496937000-8450-1-git-send-email-rodrigo.vivi@intel.com