dtb concatenation support

Since release 3.11 (actually 3.10 in some cases), kernel mandates a DTB tree to be available at boot time or it fails to boot on some boards (pandaboard in this case): to support this scenario, support for DTB concatenation was added to the Saucy/generic multiplatform kernel and the last missing bits was to teach flash-kernel how and when to attach a dtb tree to the kernel before flashing it - the attached patch achieves it adding two fields to the board database.

The two new fields are:

DTB-Kernel-Version: this is minimum kernel version after which we decide to concatenate a DTB - if the kernel version is below the version mentioned here, dtb won't be attached thus we can safely install the new flash-kernel version on a older kernel/installation - 3.5 omap4 desktop won't get dtb concatenation, while people using omap4 for server and thus updating to the latest kernel (3.11 in this case) will

DTB-Id: this is the dtb file that will be concatenated - while for panda there are at least 3 different DTBs, i tested the pandaes dtb variant with a wide range of hw revisions and it worked (tested on panda es, panda rev 4 and panda rev b1) - i'll follow up with another patch that does a run-time guessing of the correct hardware in case trouble arises

Last but not least, i had to add a new Panda entry to the board database because when you boot it with a dtb-enabled kernel, the 'Hardware' string in /proc/cpuinfo changes from 'OMAP4 Panda board' to 'Generic OMAP4 (Flattened Device Tree)'.

The attached patch is derived on the dtb-concatenation work available in the Debian repository (http://anonscm.debian.org/gitweb/?p=d-i/flash-kernel.git;a=commit;h=e7fc8e9ef6de21428acba96b8cec97744a46da6b).

Feel free to improve the shell code.