feat(imx8m): use non-fast wakeup stop mode for system suspend

Use non-fast wakeup stop mode for system suspend support, so
the SOC can enter DSM mode by default.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Change-Id: I37828d4e66ee2ebd48e7adca054b93c520cb2c82
diff --git a/plat/imx/imx8m/gpc_common.c b/plat/imx/imx8m/gpc_common.c
index 2beb35d..32a35ef 100644
--- a/plat/imx/imx8m/gpc_common.c
+++ b/plat/imx/imx8m/gpc_common.c
@@ -236,7 +236,7 @@
 
 	if (retention)
 		val |= (SLPCR_EN_DSM | SLPCR_VSTBY | SLPCR_SBYOS |
-			SLPCR_BYPASS_PMIC_READY | SLPCR_A53_FASTWUP_STOP_MODE);
+			SLPCR_BYPASS_PMIC_READY);
 
 	mmio_write_32(IMX_GPC_BASE + SLPCR, val);