drm/i915: Make HWS_NEEDS_PHYSICAL the exception

Make the .hws_needs_physical the exception by switching the flag
on earlier platforms since they are fewer to support. Remove the flag on
later GPUs hardware since they all use GTT hws by default.

Switch the logic as well in the driver to reflect this change

Signed-off-by: Carlos Santa <carlos.santa@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>