Increase system image partition size to fix build

Build of sdk_google_phone_x86_64-sdk_addon product was failing with
the following error message:

error: ext4_allocate_best_fit_partial: failed to allocate 2420 blocks,
out of space?

Change-Id: Ib9e2d21bac86b12b6f8f75d4f30806dd20abcb90
diff --git a/target/board/generic_x86_64/BoardConfig.mk b/target/board/generic_x86_64/BoardConfig.mk
index c597f7d..c4fd958 100755
--- a/target/board/generic_x86_64/BoardConfig.mk
+++ b/target/board/generic_x86_64/BoardConfig.mk
@@ -41,7 +41,7 @@
 USE_OPENGL_RENDERER := true
 
 TARGET_USERIMAGES_USE_EXT4 := true
-BOARD_SYSTEMIMAGE_PARTITION_SIZE := 880803840 # 840M
+BOARD_SYSTEMIMAGE_PARTITION_SIZE := 943718400 # 900MB
 BOARD_USERDATAIMAGE_PARTITION_SIZE := 576716800
 BOARD_CACHEIMAGE_PARTITION_SIZE := 69206016
 BOARD_CACHEIMAGE_FILE_SYSTEM_TYPE := ext4