i965: Rework Sandy Bridge HiZ and stencil layouts

Sandy Bridge does not technically support mipmapped depth/stencil.  In
order to work around this, we allocate what are effectively completely
separate images for each miplevel, ensure that they are page-aligned,
and manually offset to them.  Prior to layered rendering, this was a
simple matter of setting a large enough halign/valign.

With the advent of layered rendering, however, things got more
complicated.  Now, things weren't as simple as just handing a surface
off to the hardware.  Any miplevel of a normally mipmapped surface can
be considered as just an array surface given the right qpitch.  However,
the hardware gives us no capability to specify qpitch so this won't
work.  Instead, the chosen solution was to use a new "all slices at each
LOD" layout which laid things out as a mipmap of arrays rather than an
array of mipmaps.  This way you can easily offset to any of the
miplevels and each is a valid array.

Unfortunately, the "all slices at each lod" concept missed one
fundamental thing about SNB HiZ and stencil hardware:  It doesn't just
always act as if you're always working with a non-mipmapped surface, it
acts as if you're always working on a non-mipmapped surface of the same
size as LOD0.  In other words, even though it may only write the
upper-left corner of each array slice, the qpitch for the array is for a
surface the size of LOD0 of the depth surface.  This mistake causes us
to under-allocate HiZ and stencil in some cases and also to accidentally
allow different miplevels to overlap.  Sadly, piglit test coverage
didn't quite catch this until I started making changes to the resolve
code that caused additional HiZ resolves in certain tests.

This commit switches Sandy Bridge HiZ and stencil over to a new scheme
that lays out the non-zero miplevels horizontally below LOD0.  This way
they can all have the same qpitch without interfering with each other.
Technically, the miplevels still overlap, but things are spaced out
enough that each page is only in the "written area" of one LOD.

Cc: "17.0 17.1" <[email protected]>
Reviewed-by: Topi Pohjolainen <[email protected]>

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