libfdt: Copy the struct region in fdt_resize()

At present this function appears to copy only the data before the struct
region and the data in the string region. It does not seem to copy the
struct region itself.

>From the arguments of this function it seems that it should support fdt
and buf being different. This patch attempts to fix this problem.

Upstream commit: c72fa77 libfdt: Copy the struct region in fdt_resize()

Signed-off-by: Simon Glass <sjg@chromium.org>