drm/i915: Drop I915_PARAM_HAS_FULL_PPGTT again

At least for now userspace has no business at all to know that we
switch address spaces around. For any need it has to know whether hw
ppgtt is enabled (e.g. to set bits in MI commands correctly) it can
inquire the existing ppgtt param.

v2: Avoid ternary operator precedence fail (Chris).

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>