rcar_gen3: plat: Add missing cpu_on_check() implementation

The ATF code fails to build with PMIC_ROHM_BD9571=0, add the missing
function into the PWRC code.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
diff --git a/plat/renesas/rcar/plat_pm.c b/plat/renesas/rcar/plat_pm.c
index 245a45a..47eda9a 100644
--- a/plat/renesas/rcar/plat_pm.c
+++ b/plat/renesas/rcar/plat_pm.c
@@ -175,7 +175,7 @@
 	uint64_t cpu = read_mpidr_el1() & 0x0000ffff;
 	int32_t rtn_on;
 
-	rtn_on = cpu_on_check(cpu);
+	rtn_on = rcar_pwrc_cpu_on_check(cpu);
 
 	if (cpu == rcar_boot_mpidr)
 		panic();