db845c/BoardConfig.mk: set bootv3 as the default

enable vendor_boot by default for the db845c build

Test: boot tested with the bootv3 images

Signed-off-by: Yongqin Liu <yongqin.liu@linaro.org>
Change-Id: I792eefc4b825cb936ccd0d942fe2b94457d1e06c
diff --git a/db845c/BoardConfig.mk b/db845c/BoardConfig.mk
index d668719..5f4d343 100644
--- a/db845c/BoardConfig.mk
+++ b/db845c/BoardConfig.mk
@@ -6,6 +6,7 @@
 
 TARGET_NO_KERNEL := false
 BOARD_INCLUDE_DTB_IN_BOOTIMG := true
+TARGET_USES_BOOT_HDR_V3 ?= true
 ifeq ($(TARGET_USES_BOOT_HDR_V3), true)
  BOARD_BOOT_HEADER_VERSION := 3
  BOARD_KERNEL_PAGESIZE := 4096