ARM: mvebu: armada-xp: Consolidate pinctrl node

All current Armada XP SoCs have their pin controller at 0x18000/0x38.
Move the common properties of pinctrl nodes to armada-xp.dtsi to allow
to share pinctrl settings later.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-By: Benoit Masson <yahoo@perenite.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>