allwinner: Adjust memory mapping to fit into 256MB

At the moment we map as much of the DRAM into EL3 as possible, however
we actually don't use it. The only exception is the secure DRAM for
BL32 (if that is configured).

To decrease the memory footprint of ATF, we save on some page tables by
reducing the memory mapping to the actually required regions: SRAM, device
MMIO, secure DRAM and U-Boot (to be used later).
This introduces a non-identity mapping for the DRAM regions.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/plat/allwinner/sun50i_a64/include/sunxi_mmap.h b/plat/allwinner/sun50i_a64/include/sunxi_mmap.h
index 7d46487..28b1dd3 100644
--- a/plat/allwinner/sun50i_a64/include/sunxi_mmap.h
+++ b/plat/allwinner/sun50i_a64/include/sunxi_mmap.h
@@ -21,7 +21,7 @@
 #define SUNXI_DEV_BASE			0x01000000
 #define SUNXI_DEV_SIZE			0x01000000
 #define SUNXI_DRAM_BASE			0x40000000
-#define SUNXI_DRAM_SIZE			0x80000000
+#define SUNXI_DRAM_VIRT_BASE		0x02000000
 
 /* Memory-mapped devices */
 #define SUNXI_CPU_MBIST_BASE		0x01502000