test: Add a new benchmarker targeting affine operations

test: Add a new benchmarker targeting affine operations

Affine-bench is written by following the example of lowlevel-blt-bench.

Affine-bench differs from lowlevel-blt-bench in the following:
- does not test different sized operations fitting to specific caches,
  destination is always 1920x1080
- allows defining the affine transformation parameters
- carefully computes operation extents to hit the COVER_CLIP fast paths

Original version by Ben Avison. Changes by Pekka in v3:
- commit message
- style fixes
- more comments
- refactoring (e.g. bench_info_t)
- help output tweak

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Ben Avison <bavison@riscosopen.org>