i965: Don't forget the cube map padding on gen5+.

i965: Don't forget the cube map padding on gen5+.

We had a fixup for gen4's 3d-layout cubemaps (which, iirc, we'd
experimentally found to be necessary!), but while the spec still requires
it on gen5, we'd been missing it in the array-layout cubemaps.

Cc: "9.1 9.2" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>