feat(mediatek): add smcc call for MSDC

Some registers of MSDC need to be set in ATF, so we add MSDC drivers.

Change-Id: Idde51a136ad08dbaece0bdaa804b934fca7046b6
diff --git a/plat/mediatek/mt8186/include/platform_def.h b/plat/mediatek/mt8186/include/platform_def.h
index f3d15f3..850ce2f 100644
--- a/plat/mediatek/mt8186/include/platform_def.h
+++ b/plat/mediatek/mt8186/include/platform_def.h
@@ -72,6 +72,11 @@
 #define EMI_MPU_BASE		(IO_PHYS + 0x0021B000)
 
 /*******************************************************************************
+ * MSDC related constants
+ ******************************************************************************/
+#define MSDC0_BASE		(IO_PHYS + 0x01230000)
+
+/*******************************************************************************
  * GIC-600 & interrupt handling related constants
  ******************************************************************************/
 /* Base MTK_platform compatible GIC memory map */