Tested on:

 * Cloud Engines Pogoplug E02
 * RaidSonic ICY BOX IB-NAS62x0
 * Iomega Iconnect

Some users are avoiding to replace their bootloader, because of that add
support for second stage u-boot image. Having ubifs capable bootloader is
required in order to boot current OpenWrt trunk.

Sample ib62x0 commands for running second stage bootloader:

tftpboot 0x800000 uboot-kirkwood-ib62x0_second_stage/openwrt-kirkwood-ib62x0_second_stage-u-boot.img
bootm 0x800000

Sample ib62x0 commands for flashing second stage bootloader:

tftpboot 0x800000 uboot-kirkwood-ib62x0_second_stage/openwrt-kirkwood-ib62x0_second_stage-u-boot.img
nand erase 0x100000 0x100000 ; nand write 0x800000 0x100000 0x${filesize}
nand read 0x800000 0x100000 0x100000 ; bootm 0x800000

While at it include parallel build support, use alphabetic order of the boards
and introduce common OpenWrt configuration.

Signed-off-by: Luka Perkov <luka@openwrt.org>
Tested-by (on ib62x0): Luka Perkov <luka@openwrt.org>
Tested-by (on dockstar): Alexander Couzens <lynxis@fe80.eu>
Tested-by (on iconnect): Wojciech Dubowik <wojciech.dubowik@neratec.com>
CC: Felix Kaechele <heffer@fedoraproject.org>
CC: Wojciech Dubowik <wojciech.dubowik@neratec.com>
CC: Alexander Couzens <lynxis@fe80.eu>
CC: Daniel Engberg <daniel.engberg@pyret.net>
CC: Imre Kaloz <kaloz@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39590 3c298f89-4303-0410-b956-a3cf2f4a3e73