ARM: mvebu: Add pinctrl support to Armada XP SoCs

This commits adds the necessary device tree information to define the
compatible property for the pinctrl driver instance of Armada XP SoCs.

Until now, the device tree representation considered the Armada XP as
a single SoC. But in fact, there are three different SoCs in the
Armada XP families, with different number of CPU cores, different
number of Ethernet interfaces... and different number of muxable pins
or functions. We therefore introduce three armada-xp-mv78xx0.dtsi for
the three SoCs of the Armada XP family. The current armada-xp-db.dts
evaluation board uses the MV78460 variant of the SoC.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>