drm/tegra: hub: Implement basic scaling support

Parameterize code in several places to allow scaling of windows. Note
that this currently still relies on static programming of the various
metering and memory pool allocation registers. This seems to work for
the common cases, but may eventually need to be updated to support
use-cases with multiple windows and higher bandwidth and latency
requirements.

Signed-off-by: Thierry Reding <treding@nvidia.com>