dragonboards: Add boot image header v4 support and remove v2

Boot image header v3 remains the default header version for
db845c-userdebug builds because android11-5.4 kernel do not
have bootconfig support. To build v4 header images set
TARGET_USES_BOOT_HDR_V3=false at build time. Also removed
v2 header support for DB845c because of lack of users.

Boot image header v4 is the default header version for
rb5-userdebug builds.

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Change-Id: Icdfef0d348a87fb10a0f56f1a98490070077aa55
2 files changed