ARM: tegra: enable CPU idle for Tegra124

The CPUIdle function of Tegra124 is identical to Tegra114, so we share
the same driver with Tegra114.

Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Joseph Lo <josephl@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>