i965/miptree: Do not rely on msaa type to decide if aux is needed

i965/miptree: Do not rely on msaa type to decide if aux is needed

Once the driver moves to ISL both compressed and uncompressed have
the same type. One needs to tell them apart by other means. This
can be done by checking the existence of mcs_buf.

There is a short period of time within intel_miptree_create()
where mcs_buf doesn't exist yet (between calls to
intel_miptree_create_layout() and intel_miptree_alloc_mcs()).
First compute_msaa_layout() makes the decision if compression is
to be used and sets the msaa_layout type. Then based on the type
one sets aux_usage and finally decides if mcs_buf is needed.

This patch duplicates the logic in compute_msaa_layout() and uses
that to make the decision on aux_usage and mcs_buf allocation.
Most of the original logic in compute_msaa_layout() will be gone
in later patch leaving only one version.

Elsewhere only brw_populate_sampler_prog_key_data() needs to know
if compression is used based on the msaa_type. This is now
replaced with consideration for number of samples and existence
of mcs_buf. All other occurrences consider CMS || UMS which can
be represented using single the type of ISL_MSAA_LAYOUT_ARRAY
without any tweaks.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Topi Pohjolainen <topi.pohjolainen@intel.com>