arm64: tegra: Adapt to LP855X bindings changes

Change underscores in ROM node names to dashes, and remove deprecated
pwm-period property.

Signed-off-by: Artur Weber <aweber.kernel@gmail.com>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>