drm/i915: Drop dev from pte_encode

The original pte_encode function needed the dev argument so we could do
platform specific handling via IS_GENX, etc. With the merging of a pte
encoding function there should never been a need to quirk away gen
specific details.

The patch doesn't do much but makes the upcoming reworks in gtt/ppgtt/mm
slightly (albeit, ever so) easier.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>