linux-dtb: Add simple DTB symlinks for devicetree

linux-dtb: Add simple DTB symlinks for devicetree

* This is similar to the symlinks provided for the kernel image
  in the /boot directory of a file system.  The goal is to have
  simply named symlinks in /boot that mirror the device tree
  name in the kernel sources.  This is so that programs like
  U-Boot can easily find the default device tree binary in the
  /boot directory and use that when booting the kernel.
* Use update-alternatives to handle proper creation and removal
  of the symlinks.

(From OE-Core rev: 750a9554e1b85d9bd23d18e0630723c3c193c604)

Signed-off-by: Chase Maupin <Chase.Maupin@ti.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>