allwinner: Disable USE_COHERENT_MEM

According to the documentation, platforms may choose to trade memory
footprint for performance (and elegancy) by not providing a separately
mapped coherent page.

Since a debug build is getting close to the SRAM size limit already, this
allows us to save about 3.5KB of BSS and have some room for future
enhancements.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

plat/allwinner/common/allwinner-common.mk

@@ -52,3 +52,6 @@ SEPARATE_CODE_AND_RODATA	:=	1
 
 # BL31 gets loaded alongside BL33 (U-Boot) by U-Boot's SPL
 RESET_TO_BL31			:=	1
+
+# We are short on memory, so save 3.5KB by not having an extra coherent page.
+USE_COHERENT_MEM		:=	0

plat/allwinner/common/include/platform_def.h

@@ -27,7 +27,7 @@
 #define CACHE_WRITEBACK_SHIFT		6
 #define CACHE_WRITEBACK_GRANULE		(1 << CACHE_WRITEBACK_SHIFT)
 
-#define MAX_MMAP_REGIONS		(4 + PLATFORM_MMAP_REGIONS)
+#define MAX_MMAP_REGIONS		(3 + PLATFORM_MMAP_REGIONS)
 #define MAX_XLAT_TABLES			1
 
 #define PLAT_MAX_PWR_LVL_STATES		U(2)

plat/allwinner/common/sunxi_common.c

@@ -51,9 +51,6 @@ void sunxi_configure_mmu_el3(int flags)
 	mmap_add_region(BL_RO_DATA_BASE, BL_RO_DATA_BASE,
 			BL_RO_DATA_END - BL_RO_DATA_BASE,
 			MT_RO_DATA | MT_SECURE);
-	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);
 	mmap_add(sunxi_mmap);
 	init_xlat_tables();