Merge branch 'of_get_available_child_by_name'

Biju Das says:

====================
Add of_get_available_child_by_name()

There are lot of net drivers using of_get_child_by_name() followed by
of_device_is_available() to find the available child node by name for a
given parent. Provide a helper for these users to simplify the code.

v1->v2:
 * Make it as a series as per [1] to cover the dependency.
 * Added Rb tag from Rob for patch#1 and this patch can be merged through
   net as it is the main user.
 * Updated all the patches with patch suffix net-next
 * Dropped _free() usage.

[1]
https://lore.kernel.org/all/CAL_JsqLo4uSGYMcLXN=0iSUMHdW8RaGCY+o8ThQHq3_eUTV9wQ@mail.gmail.com/
====================

Signed-off-by: David S. Miller <davem@davemloft.net>