i965: Pretend that CCS modified images are two planes

i965: Pretend that CCS modified images are two planes

v2: move is_aux into if block. (Jason)
Use else block instead of goto (Jason)

v3: Fix up logic for is_aux (Ben)
Fix up size calculations and add FIXME (Ben)

v4 (Jason Ekstrand):
Use the aux_pitch in the image instead of calculating it

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Acked-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Chad Versace <chadversary@chromium.org>