Move the definitions of the fdt functions from a uboot header to a new fdt
header. There is nothing in the fdt spec that ties it to U-Boot.

While here sort and fix the signature of fdt_setup_fdtp.

MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273927 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f