i965: Store QPitch in intel_mipmap_tree.

i965: Store QPitch in intel_mipmap_tree.

Broadwell allows us to specify an arbitrary value for QPitch, rather
than baking a specific formula into the hardware and requiring software
to lay things out to match.  The only restriction is that the software
provided QPitch needs to be large enough so successive array slices do
not overlap.

In order to support this flexibility, software needs to specify QPitch
in a bunch of packets.  Storing QPitch makes that easy, and allows us to
adjust it in a single place should we wish to change it in the future.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Paul Berry <stereotype441@gmail.com>