loader zfs reader is missing several features, which can be supported.
Updated sha512 from illumos.
Using skein from freebsd crypto tree.
Since loader itself is using 64MB memory for heap, updated zfsboot to
use same, and this also allows to support large blocks.
Note, adding additional features does increate zfsboot code, therefore
this update does increase zfsboot code to 128k, also I have ported gptldr.S
update to zfsldr.S to support 64k+ code.
Set copy count for gptldr/zfsldr blocks to 8 - this is more than enough for
quite some time.
With little effort it is possible to add edonr, gzip would need more updates,
so to keep the changes relatively simple, I'm not adding gzip this time.