ARM: tegra: gr2d is not backwards-compatible

The instantiation of gr2d in Tegra114 is not backwards-compatible with
the version found on earlier chips. While the hardware IP is identical,
the compatible string also describes the integration of the IP, which
in the case of Tegra114 is slightly different in that it's part of the
HEG power partition, whereas it wasn't previously.

Drop the misleading compatible string so that drivers that support the
older integrations cannot match on it. Since they wouldn't be able to
control the power partition, such driver wouldn't be able to access any
of the registers of the IP.

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