Increase system image size for arm64 to 2.5G to fix buildbot

This CL increases system image size for arm64 to 2.5G to fit in the
packages.

Change-Id: I5ae52c5f64e7d54b70e36bb0bce68e8197365017
diff --git a/target/board/generic_arm64/BoardConfig.mk b/target/board/generic_arm64/BoardConfig.mk
index 129021c..455edc6 100644
--- a/target/board/generic_arm64/BoardConfig.mk
+++ b/target/board/generic_arm64/BoardConfig.mk
@@ -77,7 +77,7 @@
 USE_OPENGL_RENDERER := true
 
 TARGET_USERIMAGES_USE_EXT4 := true
-BOARD_SYSTEMIMAGE_PARTITION_SIZE := 2147483648  # 2 GB
+BOARD_SYSTEMIMAGE_PARTITION_SIZE := 2684354560  # 2.5 GB
 BOARD_USERDATAIMAGE_PARTITION_SIZE := 576716800
 BOARD_CACHEIMAGE_PARTITION_SIZE := 69206016
 BOARD_CACHEIMAGE_FILE_SYSTEM_TYPE := ext4