i965: Add plumbing for Broadwell's auxiliary surface support.

i965: Add plumbing for Broadwell's auxiliary surface support.

Broadwell generalizes the MCS fields to allow for multiple kinds of
auxiliary surfaces.  This patch adds the plumbing to set those values,
but doesn't yet hook any up.

v2: (by Jordan Justen) Use mt for qpitch; pitch is tiles - 1.
v3: Don't forget to subtract 1 from aux_mt->pitch.
v4: Drop unnecessary aux_mt->offset (caught by Jordan Justen).

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>