drm/i915: do not set MOCS control values on dgfx

On dgfx there's no LLC and eDRAM control table. Since now this
also means the device has global MOCS, just return early on the
initialization function.

L3 settings still apply and still need to be tweaked.

Bspec: 45101

Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191024195122.22877-3-lucas.demarchi@intel.com