bootimg.bbclass:hddimg: check the size of rootfs.img for hddimg
The hddimg uses FAT, so the single file size should be less than 4GB,
otherwise errors, check that and error out.
Another way might be use ext2/3/4 rather than FAT, but EFI only supports
FAT, if we make EFI use FAT, and non-EFI use extX, that would the code
very different, which seems not worth.
[YOCTO #6449]
Signed-off-by: Robert Yang <liezhi.yang@windriver.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
