Increase system partition size to 640MB

Change-Id: Ia982a4475e5e7fe8207e00f5b5025eaaa568585c
diff --git a/BoardConfig.mk b/BoardConfig.mk
index 655aa34..ae1f0ef 100755
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -77,7 +77,7 @@
 TARGET_USERIMAGES_USE_EXT4 := true
 BOARD_BOOTIMAGE_PARTITION_SIZE := 23068672 # 22M
 BOARD_RECOVERYIMAGE_PARTITION_SIZE := 23068672 # 22M
-BOARD_SYSTEMIMAGE_PARTITION_SIZE := 268435456 # 256M
+BOARD_SYSTEMIMAGE_PARTITION_SIZE := 681574400 # 640M
 
 BOARD_USERDATAIMAGE_PARTITION_SIZE := 12348030976 # 11.5G
 BOARD_FLASH_BLOCK_SIZE := 131072 # (BOARD_KERNEL_PAGESIZE * 64)