ARM: dts: Kill off skeleton{64}.dtsi

Remove the usage of skeleton.dtsi in the remaining dts files. It was
deprecated since commit 9c0da3cc ("ARM: dts: explicitly mark
skeleton.dtsi as deprecated"). This will make adding a unit-address to
memory nodes easier.

The main tricky part to removing skeleton.dtsi is we could end up with
no /memory node at all when a bootloader depends on one being present. I
hacked up dtc to check for this condition.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Antoine Tenart <antoine.tenart@bootlin.com>
Acked-by: Alexandre TORGUE <alexandre.torgue@st.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Vladimir Zapolskiy <vz@mleia.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Tested-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Tested-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>