intel/isl/gen7: Use stencil vertical alignment of 8 instead of 4

intel/isl/gen7: Use stencil vertical alignment of 8 instead of 4

The reasoning Chad gave in the comment for choosing a valign of 4 is
entirely bunk.  The fact that you have to multiply pitch by 2 is
completely unrelated to the halign/valign parameters used for texture
layout.  (Not completely unrelated.  W-tiling is just Y-tiling with a
bit of extra swizzling which turns 8x8 W-tiled chunks into 16x4 y-tiled
chunks so it makes everything easier if miplevels are always aligned to
8x8.)  The fact that RENDER_SURFACE_STATE::SurfaceVerticalAlignmet
doesn't have a VALIGN_8 option doesn't matter since this is gen7 and you
can't do stencil texturing anyway.

v2 (Jason Ekstrand):
 - Delete most of Chad's comment and add a more descriptive commit
   message.

Signed-off-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Cc: "17.0 17.1" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Chad Versace <chadversary@chromium.org>