ubldr zfs support

[fate10_gmail.com]

Summary

ubldr zfs support and some minor rewritings

Test Plan

apply patch,
add "options KSTACK_PAGES=4" to your arm kernel config,
add:

vm.kmem_size_max=800m
vm.kmem_size=512m
vfs.zfs.arc_max=550m

to /boot/loader.conf

make kernel world UBLDR_LOADADDR=0x42000000

(address is your hardware dependant, here is Allwinner A)
create zfs FreeBSD system just build on the hard disk
set loaderdev enviroment variable in u-boot to "zfs <your pool>"
or make it empty

[fate10_gmail.com]

• remove commented code from sys/boot/uboot/lib/disk.c
• whitespace correction
• update to latest HEAD