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
2 files changed