backports: backport of_get_child_by_name() support

backports: backport of_get_child_by_name() support

This was added via 9c19761a. While at it clean up the backported
header a bit to make backporting more OF stuff more manageable.

mcgrof@frijol ~/linux-stable (git::master)$ git describe --contains 9c19761a
v3.7-rc1~123^2~4

commit 9c19761a7ecdc86abb2fba0feb81e8952eccc1f1
Author: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Date:   Tue Sep 18 08:10:28 2012 +0100

    dt: introduce of_get_child_by_name to get child node by name

    This patch introduces of_get_child_by_name function to get a child node
    by its name in a given parent node.

    Without this patch each driver code has to iterate the parent and do
    a string compare, However having of_get_child_by_name libary function would
    avoid code duplication, errors and is more convenient.

    Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
    Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>