ar71xx: dragino2: add missing sysupgrade support.

The original dragino2 board support was missing some changes from the
upstream svn repository (http://svn.dragino.com/dragino2) that supported
sysupgrade.

[juhosg: change subject]

Signed-off-by: Karl Palsson <karlp@remake.is>
Patchwork: http://patchwork.openwrt.org/patch/4801/
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39429 3c298f89-4303-0410-b956-a3cf2f4a3e73
kernel/modules: add xen-privcmd package

Also select that for kmod-xen-fs. Fixes the following build
error:

  Package kmod-xen-fs is missing dependencies for the following libraries:
  xen-privcmd.ko

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39430 3c298f89-4303-0410-b956-a3cf2f4a3e73