Tegra: enable 'signed-comparison' compilation warning/errors

This patch enables the 'sign-compare' flag, to enable warning/errors
for comparisons between signed/unsigned variables. The warning has
been enabled for all the Tegra platforms, to start with.

Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>
diff --git a/lib/psci/psci_common.c b/lib/psci/psci_common.c
index 763de04..f31b323 100644
--- a/lib/psci/psci_common.c
+++ b/lib/psci/psci_common.c
@@ -332,7 +332,7 @@
 				      unsigned int node_index[])
 {
 	unsigned int parent_node = psci_cpu_pd_nodes[cpu_idx].parent_node;
-	int i;
+	unsigned int i;
 
 	for (i = PSCI_CPU_PWR_LVL + 1; i <= end_lvl; i++) {
 		*node_index++ = parent_node;
@@ -901,7 +901,7 @@
  *****************************************************************************/
 int psci_secondaries_brought_up(void)
 {
-	int idx, n_valid = 0;
+	unsigned int idx, n_valid = 0;
 
 	for (idx = 0; idx < ARRAY_SIZE(psci_cpu_pd_nodes); idx++) {
 		if (psci_cpu_pd_nodes[idx].mpidr != PSCI_INVALID_MPIDR)