Check DTB image size for boot image header version 2 and above

DTB in boot image is mandatory for boot image header version 2
and above. mkbootimg.py must check the size of the DTB image passed
to it and throw an error if the image is empty.

Test: build with no DTB files in BOARD_PREBUILT_DTBIMAGE_DIR
Bug: 133006443
Change-Id: I478fcdb8e77957848a93027e695fcb238c544d62
1 file changed