fix(ast2700): add device mapping for coherent memory

The coherent memory should be mapped as Device nGnRnE.
This fix adds the missing MMU attributes for coherent memory
if enabled.

Signed-off-by: Chia-Wei Wang <chiawei_wang@aspeedtech.com>
Change-Id: I90b8de167c48f03392c9740f88f4b1e7b073a82d
diff --git a/plat/aspeed/ast2700/plat_bl31_setup.c b/plat/aspeed/ast2700/plat_bl31_setup.c
index fde5dbb..92a48ff 100644
--- a/plat/aspeed/ast2700/plat_bl31_setup.c
+++ b/plat/aspeed/ast2700/plat_bl31_setup.c
@@ -76,6 +76,12 @@
 			BL_END - BL_CODE_END,
 			MT_RW_DATA | MT_SECURE);
 
+#if USE_COHERENT_MEM
+	mmap_add_region(BL_COHERENT_RAM_BASE, BL_COHERENT_RAM_BASE,
+			BL_COHERENT_RAM_END - BL_COHERENT_RAM_BASE,
+			MT_DEVICE | MT_RW | MT_SECURE);
+#endif
+
 	mmap_add_region(BL32_BASE, BL32_BASE, BL32_SIZE,
 			MT_MEMORY | MT_RW);