drm/i915/cfl: Basic DDI plumbing for Coffee Lake.

All here is pretty much like Kabylake.

Including CFL-U has to use same ddi translation table
as KBL-U for now.

v2: Include missed IS_COFFEELAKE on edp trans table. (DK)
    Handle CFL-U with same translation table as KBL-U. (DK and
    confirmed with HW engineers)

v3: Adding missed case for IS_CFL_ULT. (DK).

v4: Duh! Now with the real IS_CFL_ULT instead of KBL one. (DK)
    Also use IS_GEN9_BC when possible. (DK)

Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1497045770-21302-1-git-send-email-rodrigo.vivi@intel.com