Add system image size for X86

It was defaulting to 128M which was slightly too small for all the
applications. Increasing to 150M fits the resulting image.

Change-Id: I55957c54fbdb77090487c08ed3948988621978b3
diff --git a/target/board/generic_x86/BoardConfig.mk b/target/board/generic_x86/BoardConfig.mk
index 2268d41..83c2da0 100644
--- a/target/board/generic_x86/BoardConfig.mk
+++ b/target/board/generic_x86/BoardConfig.mk
@@ -20,6 +20,7 @@
 BOARD_BOOTIMAGE_MAX_SIZE := 8388608
 BOARD_SYSLOADER_MAX_SIZE := 7340032
 BOARD_FLASH_BLOCK_SIZE := 512
+BOARD_SYSTEMIMAGE_PARTITION_SIZE := 150M
 BOARD_USERDATAIMAGE_PARTITION_SIZE := 50M
 BOARD_INSTALLERIMAGE_PARTITION_SIZE := 500M
 TARGET_USERIMAGES_SPARSE_EXT_DISABLED := true