drm/i915: Allow HW status page to be bound high

At the time of commit 1f767e02 ("drm/i915: HWS must be in the
mappable region for g33"), drm_mm insertion would often default to
placing a new object high in the zone forcing us to specify that certain
HWSP must be bound within the low mappable region. Since then, drm_mm
has gained more finesse over its placement and exposes that to the
caller, commit 4e64e553 ("drm: Improve drm_mm search (and fix
topdown allocation) with rbtrees"). As such where possible we want the
HWSP to be outside of the mappable aperture and so need to specify that
can be pinned high.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170913085605.18299-4-chris@chris-wilson.co.uk