arm64: tegra: Add missing Smaug revision

The "google,smaug-rev2" string is missing from the compatible list of
Smaug's DT. The differences of rev2 are not relevant at our current
level of support and it boots just fine, so add it.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Andrew Bresticker <abrestic@chromium.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>