dtc: Don't abuse struct fdt_reserve_entry

struct fdt_reserve_entry is defined in fdt.h to exactly mirror the
in-memory layout of a reserve entry in the flattened tree.  Since that is
always big-endian, it uses fdt64_t elements, which have sparse annotations
marking them as not native endian.

However, in dtc, we also use struct fdt_reserve_entry inside struct
reserve_info, and use it with native endian values.  This will cause sparse
errors.

This stops this abuse, making struct reserve_info have its own native
endian fields for the same information.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>