isl: Rework the way we define tile sizes.

isl: Rework the way we define tile sizes.

This is based on a very long set of discussions between Chad and myself
about how we should properly represent HiZ and CCS buffers.  The end result
of that discussion was that a tiling actually has two different sizes, a
logical size in elements, and a physical size in bytes and rows.  This
commit reworks ISL's pitch and size calculations to work in terms of these
two sizes.

Reviewed-by: Chad Versace <chad.versace@intel.com>