ath79: move dts-v1 statement to ath79.dtsi

ath79: move dts-v1 statement to ath79.dtsi

The "/dts-v1/;" identifier is supposed to be present once at the
top of a device tree file after the includes have been processed.

In ath79, we therefore requested to have in the DTS files so far,
and omit it in the DTSI files. However, essentially the syntax of
the parent ath79.dtsi file already determines the DTS version, so
putting it into the DTS files is just a useless repetition.

Consequently, this patch puts the dts-v1 statement into the parent
ath79.dtsi, which is (indirectly) included by all DTS files. All
other occurences are removed.
Since the dts-v1 statement needs to be before any other definitions,
this also moves the includes to make sure the ath79.dtsi or its
descendants are always included first.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>