allwinner: Don't map boot ROM

There is nothing we need from the BootROM area, so we also don't need
to map it in EL3.

Remove the mapping and reduce the number of MMAP regions by one.

Reported-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/plat/allwinner/common/include/platform_def.h b/plat/allwinner/common/include/platform_def.h
index 2752aa4..d039188 100644
--- a/plat/allwinner/common/include/platform_def.h
+++ b/plat/allwinner/common/include/platform_def.h
@@ -39,7 +39,7 @@
 #define PLATFORM_CORE_COUNT		(PLATFORM_CLUSTER_COUNT * \
 					 PLATFORM_MAX_CPUS_PER_CLUSTER)
 #define PLATFORM_MAX_CPUS_PER_CLUSTER	4
-#define PLATFORM_MMAP_REGIONS		4
+#define PLATFORM_MMAP_REGIONS		3
 #define PLATFORM_STACK_SIZE		(0x1000 / PLATFORM_CORE_COUNT)
 
 #ifndef SPD_none