drm/i915: Turn vgpu pdps into an array

We'll want to avoid performing arithmetic with register offsets, so
instead calculating the vgpu PDP as pdp0_lo+offset, make the PDPs
into an array. This way we can simply loop through them.

Cc: Eddie Dong <eddie.dong@intel.com>
Cc: Jike Song <jike.song@intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>
Cc: Yu Zhang <yu.c.zhang@linux.intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: Zhiyuan Lv <zhiyuan.lv@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1446672017-24497-25-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Zhiyuan Lv <zhiyuan.lv@intel.com>