plat: imx8m: Keep A53 PLAT on in wait mode(ret)

Keep A53 PLAT(SCU) power domain on in wait mode(ret).
RBC count only need to be set in PLAT OFF mode, so
change it accordingly.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Change-Id: Ie55e25c8210d298506fc4dca7a9653583db45e0c
diff --git a/plat/imx/imx8m/gpc_common.c b/plat/imx/imx8m/gpc_common.c
index eb2801c..8aae1a6 100644
--- a/plat/imx/imx8m/gpc_common.c
+++ b/plat/imx/imx8m/gpc_common.c
@@ -133,14 +133,12 @@
 		val = mmio_read_32(IMX_GPC_BASE + LPCR_A53_AD);
 		val &= ~EN_L2_WFI_PDN;
 		/* L2 cache memory is on in WAIT mode */
-		if (is_local_state_off(power_state))
+		if (is_local_state_off(power_state)) {
 			val |= (L2PGE | EN_PLAT_PDN);
-		else
-			val |= EN_PLAT_PDN;
+			imx_a53_plat_slot_config(true);
+		}
 
 		mmio_write_32(IMX_GPC_BASE + LPCR_A53_AD, val);
-
-		imx_a53_plat_slot_config(true);
 	} else {
 		/* clear the slot and ack for cluster power down */
 		imx_a53_plat_slot_config(false);