drm/tegra: sor - Do not hardcode number of blank symbols

The number of HBLANK and VBLANK symbols can be computed at runtime so
that they can be set appropriately depending on the video mode and DP
link.

These values are used by the packet generation logic to determine how
many audio samples can be transferred during the blanking intervals.

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