dt-bindings: display: tegra: document Tegra30 VI and VIP

dt-bindings: display: tegra: document Tegra30 VI and VIP

Existing Parallel VI interface schema for Tegra20 is fully compatible with
Tegra30; hence, lets reuse it by setting fallback for Tegra30.

Adjust existing VI schema to reflect that Tegra20 VI is compatible with
Tegra30 by setting a fallback for Tegra30. Additionally, switch to using
an enum instead of list of const.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Tested-by: Luca Ceresoli <luca.ceresoli@bootlin.com> # tegra20, parallel camera
Signed-off-by: Thierry Reding <treding@nvidia.com>