refactor(imx8m): replace magic number with enum type

Replace those RDC config related magic numbers with enum type

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Change-Id: I6245ccfa74d079179dc0f205980c2daf5c7af786
diff --git a/plat/imx/imx8m/imx8mm/imx8mm_bl31_setup.c b/plat/imx/imx8m/imx8mm/imx8mm_bl31_setup.c
index 40110d7..71d7497 100644
--- a/plat/imx/imx8m/imx8mm/imx8mm_bl31_setup.c
+++ b/plat/imx/imx8m/imx8mm/imx8mm_bl31_setup.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2019-2022 ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -44,9 +44,11 @@
 
 static const struct imx_rdc_cfg rdc[] = {
 	/* Master domain assignment */
-	RDC_MDAn(0x1, DID1),
+	RDC_MDAn(RDC_MDA_M4, DID1),
 
 	/* peripherals domain permission */
+	RDC_PDAPn(RDC_PDAP_UART4, D1R | D1W),
+	RDC_PDAPn(RDC_PDAP_UART2, D0R | D0W),
 
 	/* memory region */