intel: Add map_stencil_as_y_tiled to intel_region_get_tile_masks.

intel: Add map_stencil_as_y_tiled to intel_region_get_tile_masks.

When the blorp engine is performing a blit from one stencil buffer to
another, it sets up the surface state for these buffers as Y-tiled, so
it needs to be able to force intel_region_get_tile_masks() to return
the appropriate masks for a Y-tiled region.

NOTE: This is a candidate for stable release branches.

Acked-by: Eric Anholt <eric@anholt.net>