of/fdt: use libfdt accessors for header data

With libfdt support, we can take advantage of helper accessors in libfdt
for accessing the FDT header data. This makes the code more readable and
makes the FDT blob structure more opaque to the kernel. This also
prepares for removing struct boot_param_header completely.

Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Tested-by: Michal Simek <michal.simek@xilinx.com>
Tested-by: Grant Likely <grant.likely@linaro.org>
Tested-by: Stephen Chivers <schivers@csc.com>
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-commit: c972de14971f1482ab482f0a7abc85679a23326a
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>