ARM: tegra: cpuidle: remove redundant parameters for powered-down mode

After the patch series for system suspending support, tegra_idle_lp2_last()
no longer uses its parameters cpu_on_time or cpu_off_time, so remove them.

Signed-off-by: Joseph Lo <josephl@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>