arm64: dts: marvell: add pinctrl support for Armada 7K/8K

Enable pinctrl support for CP and AP on the Armada 7K/8K SoCs.

The CP master being different between Armada 7k and Armada 8k. This
commit introduces the intermediates files armada-70x0.dtsi and
armada-80x0.dtsi.

These new files will provide different compatible strings depending of
the SoC family. They will also be the location for the pinmux
configuration at the SoC level.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>