arm64: tegra: Add regulators for Tegra210 Smaug

Add regulators to the Tegra210 Smaug DTS file including support for the
MAX77620 PMIC.

Signed-off-by: Rhyland Klein <rklein@nvidia.com>
Acked-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>