ARM: mvebu: set correct mem_size for db-88f6820-amc

The db-88f6820-amc has four chips with 2Gb density giving a total of 1GB
DRAM. Update the board_topology_map to reflect the correct
configuration.
Signed-off-by: NChris Packham <judge.packham@gmail.com>
Reviewed-by: NStefan Roese <sr@denx.de>
Signed-off-by: NStefan Roese <sr@denx.de>

board/Marvell/db-88f6820-amc/db-88f6820-amc.c

@@ -66,7 +66,7 @@ static struct hws_topology_map board_topology_map = {
 	      {0x1, 0, 0, 0} },
 	    SPEED_BIN_DDR_1866L,	/* speed_bin */
 	    BUS_WIDTH_8,		/* memory_width */
-	    MEM_4G,			/* mem_size */
+	    MEM_2G,			/* mem_size */
 	    DDR_FREQ_800,		/* frequency */
 	    0, 0,			/* cas_l cas_wl */
 	    HWS_TEMP_LOW,		/* temperature */