i965/cnl: Add a preliminary device for Cannonlake

i965/cnl: Add a preliminary device for Cannonlake

v2 (Anuj):
Rebased on master and updated pci ids
Remove redundant initialization of max_wm_threads to 64 * 12.
For gen9+ max_wm_threads are initialized in gen_get_device_info().

v3 (Anuj):
Move the patch to end of series.
Remove unused gt1, gt2, gt3 functions.
Remove l3_banks variable. Variable is now available on master.

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Signed-off-by: Ben Widawsky <benjamin.widawsky@intel.com>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>