drm/tegra: Add Tegra234 support to NVDEC driver

Add support for the Tegra234 version of NVDEC to the NVDEC driver.
This version sports a RISC-V controller and requires a few additional
clocks. After firmware has been loaded, the behavior is, however,
backwards compatible.

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