[LEDE-DEV] Convert ar71xx to devicetree

[p.wassi at gmx.at]

> I think it should not be too hard to support both DT and non-DT devices
> with the same kernel.

Also, in ar71xx patches, there's the
001-revert_spi_device_tree_support.patch
which was introduced by Felix when switching to 4.4.
(I've removed this patch now to get the SPI-NOR flash working)

Without knowing the reason for this patch, there'd possibly be
some need for workarounds if we wanted to have both in one kernel.

Best regards,
P. Wassi