ar71xx: generate recovery image for WNDR4300

ar71xx: generate recovery image for WNDR4300

Extended the Makefile to generate a working factory reset image
for Netgear WNDR4300. The image uses UBI with two volumes squashfs
(rootfs) and JFFS2 (rootfs_data). In order to make stock U-Boot
happy, a fake rootfs image is placed into the last erase block
of the kernel partition.

Signed-off-by: Stefan Agner <stefan@agner.ch>
[juhosg:
  - restore the NetgearNAND/initramfs macro,
  - remove unused {Squash,Ubi}fsTemplate macros,
  - remove board specific mtd options from CONFIG_CMDLINE, append the
    board specific ubi.mtd parameter to the kernel command line instead,
  - increase kernel partition size to 2MiB,
  - use board specific ini file for ubinize,
  - put jffs2 eof mark into the rootfs_data ubi volume,
  - use KDIR_TMP for temporary images,
  - use the squashfs-raw image,
  - increase kernel partition size to 2MiB,
  - use a local ubinize macro,
  - fix macro parameter comments,
  - put the fake rootfs into the last erase block of the kernel
    partition,
  - move Image/Build/NetgearNAND/buildkernel macro before
    define Image/Build/NetgearNAND,
  - don't use the wndr3700 utility, use '-M' parameter of mkimage to set
    the uImage magic,
  - use '-recovery' suffix for the generated image, it is only usable via
    the fw_recovery function of the bootloader,
  - update commit log]
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38655 3c298f89-4303-0410-b956-a3cf2f4a3e73