drm/i915: Let execlist_update_context() cover !FULL_PPGTT mode.

execlist_update_context() will try to update PDPs in a context before a
ELSP submission only for full PPGTT mode, while PDPs was populated during
context initialization. Now the latter code path is removed. Let
execlist_update_context() also cover !FULL_PPGTT mode.

Fixes: 34869776

 ("drm/i915: check ppgtt validity when init reg state")
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Michal Winiarski <michal.winiarski@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhiyuan Lv <zhiyuan.lv@intel.com>
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1486377436-15380-1-git-send-email-zhi.a.wang@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>