tests: add reg-spilling

When Intel hardware spills registers, it makes use of a buffer called
scratch space. Mesa calculates its size, but historically it has made
mistakes in this size calculation for compute shaders. Let's add a
test that fails when the scratch buffers are smaller than they need to
be, so we have a better way to detect these issues.

The last instance of this bug was detected as Aztec ruins just not
rendering at all. Having a piglit that fails would be a significant
improvement.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
6 jobs for reg-spilling in 5 minutes and 2 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Container
passed #5166614
debian

00:00:42

 
  Build
passed #5166615
build-debian

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passed #5166617
py36-tox

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passed #5166618
py37-tox

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passed #5166619
py38-tox

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passed #5166616
py.test

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