i965/miptree: Call alloc_aux in create_for_bo

i965/miptree: Call alloc_aux in create_for_bo

Originally, I had moved it to the caller to make some things easier when
adding the CCS modifier.  However, this broke DRI2 because
intel_process_dri2_buffer calls intel_miptree_create_for_bo but never
calls intel_miptree_alloc_aux.  Also, in hindsight, it should be pretty
easy to make the CCS modifier stuff work even if create_for_bo allocates
the CCS when DISABLE_AUX is not set.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Cc: "17.2" <mesa-stable@lists.freedesktop.org>