soc/tegra: pmc: Rename core power domain

CORE power domain uses name of device-tree node, which is inconsistent with
the names of PMC domains. Set the name to "core" to make it consistent.

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>