tests: Split helpers into library

Some of the helpers, such as the pattern drawing helpers or the format
lookup helpers, have potential to be reused. Move them into a separate
library to make it easier to share them.

Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>