anv/cmd_buffer: consider multiview masks for tracking pending clear aspects

anv/cmd_buffer: consider multiview masks for tracking pending clear aspects

When multiview is active a subpass clear may only clear a subset of the
attachment layers. Other subpasses in the same render pass may also
clear too and we want to honor those clears as well, however, we need to
ensure that we only clear a layer once, on the first subpass that uses
a particular layer (view) of a given attachment.

This means that when we check if a subpass attachment needs to be cleared
we need to check if all the layers used by that subpass (as indicated by
its view_mask) have already been cleared in previous subpasses or not, in
which case, we must clear any pending layers used by the subpass, and only
those pending.

v2:
  - track pending clear views in the attachment state (Jason)
  - rebased on top of fast-clear rework.

v3:
  - rebased on top of subpass rework.

v4: rebased.

v5 (Caio):
 - Rebased.
 - Initialize pending clear views to only have bits set for layers
   that exist.
 - Reset pending clear views in one go rather one bit at a time.
 - Put "last subpass for this attachment" condition in a separate
   function to simplify the conditional that resets pending_clear_aspects.

Fixes:
dEQP-VK.multiview.readback_implicit_clear.*

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>