anv: do not subtract the base layer to compute depth in 3DSTATE_DEPTH_BUFFER

anv: do not subtract the base layer to compute depth in 3DSTATE_DEPTH_BUFFER

According to the PRM description of the Depth field:

  "This field specifies the total number of levels for a volume texture
   or the number of array elements allowed to be accessed starting at the
   Minimum Array Element for arrayed surfaces"

However, ISL defines array_len as the length of the range
[base_array_layer, base_array_layer + array_len], so it already represents
a value relative to the base array layer like the hardware expects.

v2: Depth is defined as a U11-1 field, so subtract 1 from
    the actual value (Jason)

This fixes a number of new CTS tests that would crash otherwise:
dEQP-VK.pipeline.render_to_image.*

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