Documentation: Add device tree bindings for msm-id and board-id

Add DT bindings for msm-id and board-id which are used to identify the
MSM chipsets and boards.

The snapshot is taken from msm-3.10 branch as of 'commit 5555fe73aeb2
("ASoC: qdsp6v2: Remove Eagle code")'

Change-Id: I934bf4a31fa192246a4e994f4b9efee59f9c421a
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>
Signed-off-by: Runmin Wang <runminw@codeaurora.org>