Enable WITH_DEXPREOPT_BOOT_IMG_ONLY to support partial preopting

Bug: 16938924

Change-Id: Iadf3235cbd93375b8c3b89faa07d7d6c42cd6fb0
(cherry picked from commit c8030c7f4c3f550710450599d3915fb09284575a)
diff --git a/BoardConfigCommon.mk b/BoardConfigCommon.mk
index 7c2306b..7b84699 100755
--- a/BoardConfigCommon.mk
+++ b/BoardConfigCommon.mk
@@ -68,6 +68,8 @@
 TARGET_USES_SF_BYPASS := true
 TARGET_USES_C2D_COMPOSITON := true
 
+WITH_DEXPREOPT_BOOT_IMG_ONLY ?= true
+
 TARGET_USERIMAGES_USE_EXT4 := true
 BOARD_BOOTIMAGE_PARTITION_SIZE := 23068672 # 22M
 BOARD_RECOVERYIMAGE_PARTITION_SIZE := 23068672 # 22M