iris: Allocate main and aux surfaces together

iris: Allocate main and aux surfaces together

On Gen12, the CCS buffer address doesn't have to be referenced in state
packets. In the case of a stencil buffer with CCS, the kernel won't know
the location of the CCS unless an extra call is made to pin its address.
To avoid this extra call, make the CCS part of the main surface.

v2. Update comment above bo_size. (Jordan)

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>