Tegra: flowctrl: rename tegra_fc_cpu_idle() to tegra_fc_cpu_powerdn()

This patch renames the tegra_fc_cpu_idle() function to a more appropriate
tegra_fc_cpu_powerdn() to better reflect its usage.

Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>
diff --git a/plat/nvidia/tegra/include/drivers/flowctrl.h b/plat/nvidia/tegra/include/drivers/flowctrl.h
index 8bc821d..23909e8 100644
--- a/plat/nvidia/tegra/include/drivers/flowctrl.h
+++ b/plat/nvidia/tegra/include/drivers/flowctrl.h
@@ -73,8 +73,8 @@
 	mmio_write_32(TEGRA_FLOWCTRL_BASE + off, val);
 }
 
-void tegra_fc_cpu_idle(uint32_t mpidr);
 void tegra_fc_cluster_idle(uint32_t midr);
+void tegra_fc_cpu_powerdn(uint32_t mpidr);
 void tegra_fc_cluster_powerdn(uint32_t midr);
 void tegra_fc_soc_powerdn(uint32_t midr);
 void tegra_fc_cpu_on(int cpu);