db845c: Make TARGET_USES_BOOT_HDR_V3 visible to vendor package

Move TARGET_USES_BOOT_HDR_V3 build flag from db845c/BoardConfig.mk
to db845c.mk, so that TARGET_USES_BOOT_HDR_V3 flag can be used in
vendor/ firmware package' .mk files.

Needed for certain conditional PRODUCT_COPY_FILES in vendor package
to work correctly.

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Change-Id: Ia81e4cad55d7a8de20d5353e7cfd3d297fa6482c
diff --git a/db845c.mk b/db845c.mk
index a402ce2..e949af1 100644
--- a/db845c.mk
+++ b/db845c.mk
@@ -1,6 +1,8 @@
 $(call inherit-product, device/linaro/dragonboard/full.mk)
 $(call inherit-product, device/linaro/dragonboard/db845c/device.mk)
 
+TARGET_USES_BOOT_HDR_V3 ?= true
+
 # Product overrides
 PRODUCT_NAME := db845c
 PRODUCT_DEVICE := db845c