Makefile, scripts/package/builddeb: HACK: Force xargs max char length

This is based on https://patchwork.kernel.org/patch/1314931/ with an
extension to cover scripts/package/builddeb.  As hpa notes in the above
link, QEMU is at fault here not the kernel, thus making this a HACK.  A
bug against QEMU exists at
https://bugs.launchpad.net/qemu-linaro/+bug/1036645 but until a fix is
available, we need to hack around it.

Signed-off-by: Tom Rini <trini@ti.com>
Makefile: HACK: Install device trees with modules_install

In Ubuntu (see
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1030600) it has
been decided that device trees should live in
firmware/$version/device-trees/ so we need to add device tree
installation to the modules install rule following this location, as
this is the rule that is responsible for installing all firmware for
things built into the kernel.

Signed-off-by: Tom Rini <trini@ti.com>