ar71xx: stop producing -NA factory images and tag factory images with hd_id for WNDR3...

ar71xx: stop producing -NA factory images and tag factory images with hd_id for WNDR3700v2

NETGEAR doesn\92t produce a distinct North American image for
WNDR3700v2, they use the same image worldwide. This is a change from
earlier models such as WNDR3700 (v1). NETGEAR's v2 images now contain
an "hd_id" parameter, as well. All observed WNDR3700v2, WNDR3800, and
WNDRMAC images use 29763654+16+64 as their hd_id value.

This patch changes the OpenWrt WNDR3700v2 "factory" image generation
to stop producing the extraneous -NA version and to tag the image with
the same hd_id used in NETGEAR's images.

There is no change to WNDR3700 (v1) image generation, as NETGEAR
continues to produce distinct -NA and worldwide images, neither of
which are tagged with hd_id.

Signed-off-by: Mark Mentovai <mark@moxienet.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@27053 3c298f89-4303-0410-b956-a3cf2f4a3e73