drm/i915: change intel_fill_fb_ggtt_view() to use the real tile size

Use the actual tile size as to compute stuff in
intel_fill_fb_ggtt_view() instead of assuming it's PAGE_SIZE. I suppose
it doesn't matter since we don't use the results on gen2 platforms
where the tile size is 2k.

v2: Update due to CbCr plane

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1452625717-9713-5-git-send-email-ville.syrjala@linux.intel.com