Enable WITH_DEXPREOPT_BOOT_IMG_ONLY to support partial preopting

Bug: 16938924

Change-Id: Iadf3235cbd93375b8c3b89faa07d7d6c42cd6fb0
(cherry picked from commit 5ee6dc2752f887550cde7134d1b94e4264b1bc2a)
diff --git a/BoardConfig.mk b/BoardConfig.mk
index 2d8b178..a56770d 100644
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -68,6 +68,8 @@
 TARGET_USES_SF_BYPASS := true
 TARGET_USES_C2D_COMPOSITON := true
 
+WITH_DEXPREOPT_BOOT_IMG_ONLY ?= true
+
 TARGET_RECOVERY_FSTAB = device/lge/mako/fstab.mako
 TARGET_USERIMAGES_USE_EXT4 := true
 BOARD_BOOTIMAGE_PARTITION_SIZE := 23068672 # 22M